Methods for controlling charge accumulation while operating a mobile platform immersed in a hazardous, non-conductive substance

ABSTRACT

A mobile platform uses a charge accumulation control system to control a charge accumulation while the mobile platform is in the tank. Alternatively or additionally, the mobile platform includes a retrieval system having a buoyant body, a primary tether, and a secondary tether. Alternatively or additionally, an electrical cable is used to reduce a voltage difference between the mobile platform and the tank or other structure by electrically connecting to an electrically conductive member on the mobile platform.

TECHNICAL FIELD

Generally, this disclosure relates to devices and related methods forhandling a mobile platform in a tank containing hazardous substancesthat may be non-conductive.

BACKGROUND

Otherwise routine tasks may become exceedingly difficult if the ambientconditions pose a potential hazard to humans and/or the machineryrequired to perform those tasks. One such task is inspecting thestructural integrity of tanks used to contain flammable substances suchas liquid or gaseous hydrocarbons. Tank inspections typically includemeasuring the wall thicknesses at multiple locations of the tankstructure. An out-of-norm thickness indicates the presence of corrosion,or some other type of damage, which left unchecked could create leakpaths for the resident fluids. Unfortunately, inspections of wallsmaking up a bottom or floor of a tank must be conducted from theinterior of the tank in order to accurately assess the condition ofthese walls.

A common approach to performing tank inspections is to use human workcrews who enter the tank interior and scan the floors of tanks usingmagnetic and ultrasonic sensors. The tank must first be emptied ofliquid contents and purged of all flammable substances to a sufficientlylow concentration so that any sparks caused by equipment used by thework crews do not cause an explosion. The preliminary step of purgingthe tank is time consuming. Moreover, the tank must be decommissionedand taken out of service during the entire inspection process. Thus,manual tank inspections can be costly and disruptive to the ongoingoperations of tank owners.

A recently developed method to inspect tanks proposed by PETROBOTutilizes a remotely operated inspection device that can scan the bottomof tanks. A flexible umbilical physically and operationally connects theinspection device to a control unit, which is positioned outside of thetank. An inert gas, such as nitrogen, is pumped via the umbilical intothe inspection device before and while the inspection device is in thetank. The inert gas, which displaces the oxygen inside the inspectiondevice, is believed to minimize the likelihood of a spark igniting theflammable substance. The umbilical is also used for bi-directionalcommunication. Data collected by the inspection device can betransmitted via the umbilical to the external control unit. A humanoperator at the external control unit transmits control signals via theumbilical to steer the inspection device. In addition to gas andsignals, electrical power is conveyed by the umbilical. This system mayeliminate the need for human work crews inside the tank.

However, remotely operated inspection devices such as the PETROBOTdevice appear to be labor intensive to operate due to, for example,human control of steering during inspection operations. Moreover, theneed for an opening to accommodate the umbilical during operationpresumably exposes the outside environment to the hazardous materialsinside the tank. Thus, the need remains to more efficiently and safelyconduct inspections of tanks used to contain flammable material.

In some aspects, the present disclosure addresses these and otherdrawbacks of systems and methods for performing tank inspections in anenvironment having flammable or combustible substances. However,inspections of wall thicknesses of a tank containing a flammablesubstance is only illustrative of the general problem of performingtasks in an environment that may be harmful to humans and/or machinery.For example, toxic materials, while not necessarily flammable, may posedifficulties when conducting manufacturing or processing operations.Therefore, in further aspects, the present disclosure addresses the needto more efficiently and safely perform one or more tasks in a hazardousenvironment.

Some ambient conditions may include energetic substances that may alsobe non-conductive. The non-conductivity of an environment in whichmachinery is to be used may pose additional considerations in handingand operating such machinery. For example, the non-conductiveenvironment may not allow an electrical charge that accumulates onmachinery during operation to dissipate prior to retrieval. Thisaccumulated electrical charge may cause a spark if the machinery issufficiently close to a body with which it has a voltage differential.Such a spark may ignite an energetic substance, if present.

In aspects, the present disclosure addresses these and other drawbacksof systems and methods that utilize machinery in an environment havingenergetic substances that may be non-conductive. In some aspects, thepresent disclosure addresses such drawbacks by controlling electricalcharge accumulation on such machinery. In some aspects, the presentdisclosure addresses such drawbacks by reducing an accumulatedelectrical charge on such machinery prior to or during retrieval.

Tanks are sometimes specifically designed to restrict access into aninterior in which substances are stored in order to provide a sealed orisolated environment of such substances. For example, a tank may includea relatively small hatch, which is easily sealed, to allow personnel toaccess the tank interior. Personnel may encounter difficulties inreaching locations that are not in the immediate vicinity of that hatch.

In some aspects, the present disclosure addresses the drawbacks ofsystems and methods for deploying and retrieving equipment used incontainers, such as tanks, that have limited access to interiorlocations in such containers. In some aspects, the present disclosureaddresses the drawbacks of systems and methods for handling andretrieving machinery having an accumulated electrical charge due to usein containers that store non-conductive substances.

SUMMARY

The present disclosure, in part, relates to methods and related systemsfor handling a mobile platform in a tank containing non-conductivehazardous substances. By “non-conductive” or “electricallynon-conductive,” it is meant an electrical conductivity less than 1,000picosiemens per meter (pS/m). By way of comparison, common drinkingwater is more than one thousand times as conductive as a substancedefined as non-conductive in this disclosure.

In still further aspects, the present disclosure provides methods forretrieving a mobile platform from a tank containing non-conductivehazardous substances. An illustrative method of retrieving a mobileplatform from a tank having a hatch and at least partially filled with anon-conductive, energetic substance may include the step of: configuringthe mobile platform to include at least: an enclosure, at least onecontrol unit positioned inside the enclosure, at least one propulsionsystem positioned at least partially inside the enclosure, at least onepower supply positioned inside the enclosure, and at least one retrievalsystem disposed at least partially on the enclosure and including atleast: at least one buoyant body, at least one primary tether connectedto the at least one buoyant body and to the enclosure; at least onesecondary tether connected to the at least one buoyant body and to theenclosure.

The method may further include the steps of: predetermining a buoyantbody retrieval zone within the tank, wherein the buoyant body retrievalzone is below the hatch; lowering the mobile platform into the tankusing a deployment carrier; submerging the enclosure in anon-conductive, liquid energetic substance; moving the mobile platformusing the propulsion system to perform at least one task in the tank;releasing the at least one buoyant body and the at least one primarytether from the enclosure; positioning the released at least one buoyantbody within the buoyant body retrieval zone by using the at least oneprimary tether; accessing the at least one buoyant body through thehatch; retrieving the at least one primary tether by using the at leastone buoyant body; using the at least one primary tether to release theat least one secondary tether; and inserting a retrieval member throughthe hatch to retrieve at least one of: (i) the at least one buoyantbody, (ii) the at least one primary tether, and (iii) the at least onesecondary tether.

In further aspects, the present disclosure provides methods forneutralizing charge accumulation on a mobile platform in a tankcontaining non-conductive hazardous substances. An illustrative methodof retrieving a mobile platform from a tank at least partially filledwith a non-conductive, energetic substance may include the steps of:configuring the mobile platform to include at least: an enclosure, atleast one control unit positioned inside the enclosure, at least onepropulsion system positioned at least partially inside the enclosure, atleast one power supply positioned inside the enclosure, at least oneretrieval system disposed at least partially on the enclosure, the atleast one retrieval system including at least one buoyant body, anelectrically conductive member, and at least one tether, the at leastone tether having a portion that is not conductive, the at least onetether electrically isolating the at least one buoyant body from theenclosure; lowering the mobile platform into the tank using a deploymentcarrier; submerging the enclosure in a non-conductive, liquid energeticsubstance; and moving the mobile platform using the propulsion system toperform at least one task in the tank.

The method may further include the steps of releasing the buoyant bodyto convey the at least one tether toward a surface of thenon-conductive, liquid energetic substance; conveying an electricallyconductive cable to the electrically conductive member of the mobileplatform using the at least one tether; electrically connecting avoltage neutralizing end of the electrically conductive cable to avoltage differential neutralizing body in a spark inhibiting ambientcondition; electrically connecting a mobile platform end of theelectrically conductive cable to the electrically conductive member ofthe mobile platform while the electrically conductive member is belowthe surface of the non-conductive, liquid energetic substance; andretrieving the mobile platform from inside to outside of the tank.

In aspects, the present disclosure provides methods for controllingcharge accumulation on a mobile platform in a tank containingnon-conductive hazardous substances. An illustrative method of operatinga mobile platform in a tank at least partially filled with anon-conductive, energetic substance may include the steps of:configuring the mobile platform to include at least: an enclosure, atleast one control unit positioned in the enclosure, at least onepropulsion system at least partially positioned in the enclosure, atleast one electrical power supply positioned in the enclosure, wherein apower supplied from the at least one electrical power supply to at leastone electrical power consumer associated with the mobile platform addsan electrical charge to the mobile platform), at least one retrievalsystem disposed at least partially on the enclosure and including atleast one buoyant body, and at least one charge accumulation controlsystem disposed at least partially on the enclosure, the at least onecharge accumulation control system being configured to control anaccumulation of the electrical charge on the mobile platform by one of:(i) reducing the supplied power and preventing an increase in thesupplied power later while the mobile platform is inside the tank, and(ii) disengaging the at least one electrical power consumer from thesupplied power and preventing a reengagement of the supplied power withthe at least one electrical power consumer later while the mobileplatform is inside the tank; lowering the mobile platform into the tankusing a deployment carrier; submerging the enclosure in anon-conductive, liquid energetic substance; and moving the mobileplatform using the propulsion system to perform at least one task in thetank.

The method may further include the steps: controlling the electricalcharge accumulation on the mobile platform using the at least one chargeaccumulation control system and indicating an activation state of thecharge accumulation control system by releasing at least one buoyantbody from the enclosure, the activation state being one of: (i) prioractivation of the charge accumulation control system, and (ii)activation of the charge accumulation control system after apredetermined time delay; and retrieving the mobile platform from insideto outside of the tank.

The above-recited example of features of the disclosure have beensummarized rather broadly in order that the detailed description thereofthat follows may be better understood, and in order that thecontributions to the art may be appreciated. There are, of course,additional features of the disclosure that will be described hereinafterand which will form the subject of the claims appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

For detailed understanding of the present disclosure, references shouldbe made to the following detailed description of the disclosure, takenin conjunction with the accompanying drawings, in which like elementshave been given like numerals and wherein:

FIG. 1 sectionally illustrates a tank that may be inspected by using amobile platform according to the present disclosure;

FIG. 2 is a functional block diagram of one embodiment of a mobileplatform in accordance with the present disclosure;

FIGS. 3A-C illustrate one embodiment of an enclosure for a mobileplatform according to the present disclosure;

FIG. 4 is a functional block diagram of a control unit and certainrelated elements for a mobile platform according to one embodiment ofthe present disclosure;

FIGS. 5A-E illustrate embodiments of a marker detector that detectsmarkers according to the present disclosure;

FIG. 6A is a flow chart depicting an illustrative method for controllingthe mobile platform according to one embodiment of the presentdisclosure;

FIG. 6B illustrates a bottom wall of a tank having discontinuitiesdetected by a mobile platform in accordance with one embodiment of thepresent disclosure;

FIG. 7 schematically illustrates a propulsion system according to oneembodiment of the present disclosure that uses a pressurized interior;

FIG. 8 isometrically illustrates a power supply according to oneembodiment of the present disclosure;

FIGS. 9A-B schematically illustrate a task module adapted with sensorsin accordance with one embodiment of the present disclosure;

FIG. 10 schematically illustrates a switch assembly in accordance withone embodiment of the present disclosure;

FIGS. 11A-B schematically illustrate retrieval modules in accordancewith embodiments of the present disclosure;

FIGS. 11C-D schematically illustrate devices that may be used tofacilitate deployment and/or retrieval of a mobile platform inaccordance with embodiments of the present disclosure;

FIGS. 12A-B isometrically illustrate another embodiment of a mobileplatform in accordance with the present disclosure;

FIG. 13 is a functional block diagram of another control unit for aplatform according to one embodiment of the present disclosure;

FIG. 14 illustrates a bottom wall of a tank along which the FIG. 13embodiment steers a mobile platform in accordance with one embodiment ofthe present disclosure;

FIG. 15 is a flow chart depicting an illustrative method for using themobile platform to perform a task according to one embodiment of thepresent disclosure;

FIGS. 16A-B sectionally illustrate the deployment, release, andretrieval of a mobile platform during the performance of the FIG. 15method according to embodiments of the present disclosure;

FIG. 17 is a partial sectional view of a tank having active markersaccording to embodiments of the present disclosure;

FIGS. 18A-B are flow charts illustrating alternate methods for steeringmobile platforms according to the present disclosure;

FIG. 19 illustrates a system for retrieving a mobile platform using aprimary and a secondary tether according to an embodiment of the presentdisclosure;

FIGS. 20A-B schematically illustrate an embodiment wherein a primary anda secondary tether are connected to a buoyant body according to thepresent disclosure.

FIG. 20C schematically illustrates an embodiment wherein a tether isstored and released from a buoyant body according to the presentdisclosure;

FIG. 21 is a flow chart illustrating an embodiment of a retrieval methodaccording to the present disclosure that uses the systems and devices ofFIG. 19 and FIGS. 20 A-C;

FIG. 22 illustrates a system for retrieving a mobile platform thatreduces an electrical charge on the mobile platform according to anembodiment of the present disclosure;

FIG. 23 illustrates an electrical connection between an electricallyconductive cable and an electrically conductive member on an enclosureof a mobile platform according to embodiments of the present disclosure;

FIG. 24 is a flow chart illustrating a retrieval method according to oneembodiment of the present disclosure that uses the FIG. 22 system;

FIGS. 25A-B are flow charts illustrating alternate steps for makingelectrical connections when using the FIG. 24 method;

FIG. 26 illustrates a charge accumulation control system for a mobileplatform according to an embodiment of the present disclosure;

FIG. 27 is a flow chart illustrating a retrieval method according to oneembodiment of the present disclosure that uses the system of FIG. 26;

FIG. 28 is a flow chart illustrating alternate steps for activating thecharge accumulation control system according an embodiment of thepresent disclosure; and

FIG. 29 is a flow chart illustrating exemplary steps for controlling acharge accumulation on a mobile platform according an embodiment of thepresent disclosure.

DETAILED DESCRIPTION

The present disclosure provides devices, systems, and methods forperforming tasks in a hazardous environment. For conciseness andclarity, the description below is principally directed to systems andrelated methods for inspecting a tank structure having an interior inwhich energetic materials such as hydrocarbon fluids are present. Thepresent disclosure also provides devices, systems, and methods forhandling mobile platforms used in a non-conductive, energetic substance.For conciseness and clarity, the description below is principallydirected to systems and related methods for handling mobile platforms ina tank structure having an interior in which non-conductive, energeticsubstances, such as some classes of hydrocarbon liquids and gases, arepresent. However, it is emphasized that the present teachings can bereadily applied to other industries and uses.

Referring initially to FIG. 1, a tank 10 may be used to store anenergetic substance, such as hydrocarbons, in the form of a liquid body12 and a vapor 14. The fluid-tight tank may include a domed top wall 16,a generally planar bottom wall 18, and a cylindrical vertical wall 20.An interior 22 of the tank 10 may be accessed via a hatch 24. In sometanks, pillars 26 may be used for structural support or other uses.Also, it is common for the tank 10 to also contain objects 27, which maybe intentionally placed such as sumps, piping, supports, etc. or foreignmaterial such as debris, dropped tools, chains, wires, etc. The tank 10may be a fixed above-ground tank or an underground tank. The tank 10 mayalso be positioned on a vehicle or vessel such as a barge, ship, landvehicle, etc. Moreover, the tank 10 may employ different configurations;e.g., the top wall 16 may be flat and/or an interior floating roof maybe used. As will be evident from the discussion below, systems andmethods of the present disclosure can perform inspections of the tank10, and other similar structures irrespective of their usage, location,or design, with greater efficiency and safety than conventional tankinspection devices and methods.

Referring now to FIG. 2, there is shown, in functional block diagramformat, a non-limiting embodiment of an intelligent mobile platform 100for performing one or more tasks in the tank 10 of FIG. 1. The mobileplatform 100 may include an enclosure 200, a control unit 300, apropulsion system 400, and a power supply 500. Optionally, a task module600 may also be carried by the mobile platform 100. As used herein, theterm “carried by” means that the object is inside, attached to, or onthe mobile platform 100. Hereafter, these structures and on-boardequipment will collectively be referred to as “subsystems.” In someembodiments, the control unit 300 has bi-directional communication withone or more subsystems via a communication network 360. In otherembodiments, communication may be in one direction to one or moresubsystems. In still other embodiments, no communication is provided toor from some of the subsystems. The power supply 500 supplies power toone or more systems via a power distribution network 362, which mayshare circuitry with the communication network 360. The mobile platform100 may be considered “intelligent” because the control unit 300 isconfigured to control the subsystems of the mobile platform 100 by usingonly previously programmed instructions and information acquired “realtime” or “near real time” via on-board sensing instruments. That is, themobile platform 100 can acquire information relevant to an assigned taskand make decisions in furtherance of the completion of that task withouthuman intervention. Therefore, advantageously, the mobile platform 100may not have and may not require any umbilical, physical or otherwise,to a location external to a tank through which power or command signalsare received. The subsystems of the mobile platform 100 are discussed ingreater detail below.

Generally, the mobile platform 200 is configured to be inherently safe.By “inherently safe,” it is meant that the mobile platform 200 isdesigned such that at no time during operation in the tank 10 (FIG. 1)will a spark from the mobile platform 200 come into contact with theenergetic substance outside of the mobile platform 200. An element ofthe “inherently safe” design is that the enclosure 200 incorporatesstructural features that prevent a spark, or a spark from an explosionof the energetic substance 12, 14, or a spark from an explosion ofanother energetic substance similar to the energetic substance 12, 14,occurring inside the enclosure 200 under normal operating and standardatmospheric conditions (i.e., twenty degrees Celsius (sixty-eightdegrees Fahrenheit) and 1.01325 bar) from passing to an exterior of theenclosure 200. Another energetic substance is considered to be “similar”to the energetic substance 12, 14 if such other energetic substance hasa Maximum Experimental Safe Gap (MESG) in the same class as theenergetic substance 12, 14 (such class specified as: i. less than orequal to 0.45 mm (17.72 mils), ii. greater than 0.45 mm (17.72 mils) andless than or equal to 0.75 mm (29.53 mils), or iii. greater than 0.75 mm(29.53 mils)) and/or has a Minimum Igniting Current Ratio (MICR) in thesame class as the energetic substance 12, 14 (such class specified as:i. less than or equal to 0.4, ii. greater than 0.4 and less than orequal to 0.8, or iii. greater than 0.8).

An “intrinsically safe” component is one that cannot create a spark whenused as intended for the purpose for which the component was designed. A“non-intrinsically safe” or “spark-generating” component may generate aspark when operated as intended. The interior of the enclosure 200houses all components of a device, assembly, or subassembly that are notintrinsically safe; i.e., all “spark-generating” components. Thus, theenclosure 200 may be considered an “inherently safe” structure.

Generally, “spark-generating components” include mechanical structuresthat move fast enough to cause a spark and electrical components thatoperate at sufficiently high energy state to cause sparking. Generally,“non spark-generating components” include mechanical structures that donot move fast enough to cause a spark and electrical components thatoperate at sufficiently low energy state to preclude sparking. It shouldbe noted that some subsystems may include spark-generating andnon-spark-generating components. The mobile platform 100 is designedsuch that spark-generating components of such subsystems are positionedinside the enclosure 200. The non-spark-generating components of suchsubsystems may be positioned internal or external to the enclosure 200.By way of example, the propulsion system 400 has spark-generatingcomponents isolated inside the enclosure 200 and intrinsically safeexternal components external to the enclosure 200.

As described below, the enclosure 200 uses construction techniques andmaterials that ensure that sparks from a spark-generating component, orsparks from explosions caused by such sparks, do not pass to theexterior of the enclosure 200 and ignite any ambient energetic material.

Referring to FIG. 3A, there is shown one enclosure 200 according to thepresent disclosure. While the enclosure 200 is shown as a singleintegral body, the enclosure 200 may have two or more separate and fullyself-contained bodies. The enclosure 200 includes a shell 202 and a toplid 204. The shell 202 is defined by a side wall 220 and a bottom 206,which collectively define an interior 208. The vertical wall 220 andbottom 206 may be formed as an integral body or an assembly ofindividual walls. The outer shell 200 may be formed as an elongated box.However, other shapes, and combination of shapes, such as spherical,frustoconical, or cylindrical may be used. Moreover, the enclosure 200may incorporate planar, curvilinear, and/or asymmetric geometries.Suitable materials for the enclosure 200 include metals, alloys,polymers, glass, composites, and combinations thereof. Additionally, theenclosure 200 may be liquid-tight so that the mobile platform 100 (FIG.2) can be partially or fully submerged in the liquid body 12 (FIG. 1)inside the tank 10 (FIG. 1).

Referring to FIG. 3B, the walls 220 and internal structures of theenclosure 200 may use a range of thicknesses. The walls may be formed asplates, ribs, meshes, etc. Selected areas may be strengthened usingreinforcement members such as steel rings (not shown). In somesituations, it may be desirable that the enclosure 200 use features suchas fillets and symmetric arrangements to manage or control stressconcentrations in the enclosure 200. For example, the interior 208 issymmetrically arranged in the longitudinal and transverse axes.Depending on the application, the symmetry may be along one, two, orthree axes. For purposes of the present disclosure, the symmetry doesnot require identical features (e.g., volumes or dimensions) on eachside of an axis. Rather, the interior 208 may be considered symmetric ifboth sides of an axis cause a spark or related explosion to dissipate ingenerally the same manner (e.g., rate of propagation/dissipation,direction of movement, etc.).

The enclosure 200 may also use structures that disrupt detonation pathssuch as interior baffles, orthogonal corners, and shields in front ofrelatively weak wall sections and/or portals or other passages leadingto the exterior of the enclosure 200. For example, a majority of cornersof the shell 202 that define the interior 208 can have a ninety-degreeangle. Other arrangements may have more than sixty percent or eightypercent of such corners having a ninety-degree angle. Additionally, oneor more interior plates 222 may be positioned to divide the volume ofthe interior 208 to reduce the length of pathways that pressure wavescan travel unobstructed across the interior 208. These interior plates222, which may be referred to as baffles or blast shields, createcircuitous paths that can dissipate shock waves.

Referring to FIGS. 3A-C, in embodiments, the lid 204 may be removablyaffixed to a top surface 224 of the vertical wall 220 with a pluralityof fastening elements 226. The fastening elements 226 may be distributedcontinuously along a perimeter of the lid 204 to provide a nearlyuniform compressive/clamping force that secures the lid 204 to the shell202. In some arrangements, the fastening elements 226 are spaced apartsuch that the interstitial length is at a defined maximum fraction of alength along which the fastening elements 226 are distributed. Forexample, if the defined maximum fraction is one-twentieth and the lengthof a perimeter along which the fastening elements 226 are distributed isone meter, then fastening elements 226 are distributed such that nofastening element 226 is more than five centimeters from one anotherfastening element 226. In embodiments, the maximum defined fraction maybe one-half, one-quarter, one-fifth, an eighth, or a tenth of a lengthalong which the fasteners are distributed. A fastening element 226 maybe any member that connects to the shell 202 and applies a compressiveforce that presses the lid 204 against the shell 202. Fastening elements226, include screws, bolts, clamps, rivets, etc.

In one embodiment, the enclosure 200 incorporates one or more of theabove described structural features, and/or other known structuralfeatures, to prevent permanent structural deformation upon encounteringa specified pressure for a specified time in the interior 208 of theenclosure 200. The specified pressure and duration may be based on theanticipated use for the mobile platform 100 and selected to simulate amaximum stress imposed on the enclosure 200 should an explosion occurduring operation. In some applications, a “permanent structuraldeformation” is a plastic deformation that forms a path between theinterior 208 and an exterior of the enclosure 200. The path, which maybe caused by a loosening of joints or bursting of the enclosure 200, mayallow a spark to be communicated to the exterior of the enclosure 200.In embodiments, the specified pressure and duration may be at least tenbars for at least ten seconds, a pressure of at least eight bars for atleast eight seconds, a pressure of at least six bars for least sixseconds, a pressure of three and one-half bars for at least ten seconds,or a pressure of at least four bars for at least four seconds.

In addition to pressure resistance, the enclosure 200 may incorporatefurther features to allow operations in particular types of tanks.Referring to FIG. 1, the mobile platform 100 may be sized for entry intoand out of a tank 10 having openings and associated hatches 24 ofdifferent shapes and relatively limited sizes. The dimensions ofopenings and related reinforcement structures take into account fallprotection, anchorage, hoisting, or personnel retrieval. Experiencedengineers may size openings as appropriate for a particular application.Nevertheless, some standardized openings are used. For example, someparallelogram-shaped openings may have maximum dimensions of 36 inches(914.4 mm) by 72 inches (1,828.8 mm). Other parallelogram-shapedopenings may have maximum dimensions of 36 inches (914.4 mm) by 36inches (914.4 mm). Also, some circular openings may have a maximumdiameter of 23.62 inches (600 mm), 24 inches (609.4 mm), or 36 inches(914.4 mm). Therefore, in embodiments, mobile platforms 100 of thepresent disclosure may be sized to pass through a parallelogram-openinghaving a width no larger than 36 inches (914.4 mm) and a length nolarger than 72 inches (1,828.8 mm) or a width no larger than 36 inches(914.4 mm) and a length no larger than 36 inches (914.4 mm). In otherembodiments, mobile platforms 100 of the present disclosure may be sizedto pass through a circular opening no larger than 36 inches (914.4 mm)in diameter, a circular opening no larger than 24 inches (609.6 mm) indiameter, or a circular opening no larger than 600 mm (23.62 inches) indiameter.

Further, in embodiments, the overall weight of the mobile platform 200may be maintained at or below a value that could impose difficultiesduring handling or damage the bottom wall 18 of the tank 10. Inembodiments, the overall weight of the mobile platform 100 may be below10,000 pounds (4,536 kg). In other embodiments, the overall weight ofthe mobile platform 100 may be below 6,000 pounds (2,722 kg).

Thus, the construction of the enclosure 200 may be bounded by pressureresistance requirements, maximum size requirements, and maximum weight.Construction techniques for making enclosures resistant to rapidincreases in pressure are known in the art; e.g., U.S. Pat. No.2,801,768, Explosion proof Enclosure; U.S. Pat. No. 6,452,163, ArmoredDetector Having Explosion Proof Enclosure; U.S. Pat. No. 8,227,692,Explosion-Proof Enclosure; WO 2017003758, Improved Explosive-ProofThermal Imaging System; and EP 2418926, Sheet Metal Explosion-Proof andFlame-Proof Enclosures. Thus, for conciseness, details of suchconstruction features will not be discussed in further detail. It isemphasized that the above-described construction techniques are merelyillustrative of known techniques for configuring the enclosure 200 to beinherently safe. Enclosures 200 encompassed by the present disclosuremay incorporate some or all of the above-features or incorporate onlyother known construction techniques.

Additionally, the enclosure 200 may include two or more separate housingstructures. These structures may have the same or similar features andhouse spark-generating components. For example, one or more additionalseparate enclosures may house lights and associated batteries to assistwith camera images, sensors, tooling, etc. The additional enclosure(s)may be bolted onto the enclosure 200, attached with a tether, towedseparately in a wagon type of arrangement, or otherwise physicallyconnected.

Referring to FIG. 4, there is shown one non-limiting embodiment of anintelligent control unit 300 that is programmed to control one or morefunctions of the mobile platform 100 (FIG. 2). The control unit 300 mayinclude a processor module 302 and a navigation module 304. While thecontrol unit 300 may be discussed in the singular, it should beunderstood that the control unit 300 may be configured as a group of twoor more discrete programmed processing devices that work independentlyor collectively. Moreover, these discrete processing devices may beeither distributed throughout the enclosure 200, in separate enclosures,or centralized in one location.

The processor module 302 may include pre-programmed algorithms 303 forcontrolling some or all of the mobile platform 100. By way of exampleand not limitation, these algorithms 303 may be executed to issuecontrol signals 308 for operating the propulsion system 400, controlsignals 310 to manage the power supply 500, and control signals 312 foroperating one or more task modules 600. For example, information 309relating to the power supply 500 may be used to manage powerdistribution. As used herein, an algorithm means instructions stored ina memory module that can be accessed and implemented by aprocessor-based machine. The processor module 302 may use conventionalmicro-processors, memory modules that store one or more databases, 303a,b and other known components of information processing devices.

The navigation module 304 may be configured to acquire information thatmay be used to determine a position of the mobile platform 100 and/or aposition relative to a feature associated with a tank 10 (FIG. 1) and/oran orientation of the mobile platform 100. For brevity, the term“position” is inclusive of an orientation (e.g., heading, tilt, azimuth,etc.) and location (i.e., a point relative to an external referenceframe such as a Cartesian coordinate system or a polar coordinatesystem). A “relative” position is a position identified by referencing aprevious position. In one embodiment, the navigation module 304 mayinclude a marker detector liquid that generates signals in response to adetected feature associated with the tank 10 (FIG. 1). The markerdetector 306 may be passive or active as discussed in connection withFIGS. 5A-E below. The feature may be either structural or added to thetank 10 (FIG. 1). One non-limiting example of such a feature is adiscontinuity found at the juncture of two or more steel plates fromwhich a tank wall is formed; e.g., the bottom wall 18 shown in FIG. 1.The marker detector embodiments discussed herein below use differenttechniques to detect the discontinuity, which manifests itself as achange in a material property, composition, and/or dimension.

Referring to FIGS. 5A-E, there are shown five non-limiting detectorarrangements for detecting features such as discontinuities. FIG. 5Aillustrates the mobile platform 100 during contact with a discontinuity320 on an inner surface 322 of a tank 10 (FIG. 1). The mobile platform100 prior to encountering the discontinuity 320 is shown in dashedlines. The discontinuity 320 may include a weld seam 325 at a junctureof two overlapping plates 324, 326. The mobile platform 100 may have amarker detector 306 (FIG. 4) that senses orientation, such as aninclinometer 328. Other orientation sensing devices may includeaccelerometers and gyroscopes. During contact with the discontinuity320, the inclinometer 328 will sense a change in inclination andgenerate a responsive signal. The control unit 300 (FIG. 4) can processthe signal to determine if the detected signals are indicative of ajuncture between two plates or some other discontinuity. The FIG. 5Aarrangement may be considered a passive system because no energy isemitted to detect the discontinuity 320.

In FIG. 5B, the mobile platform 100 includes a signal emitter 330 thatemits an energy wave 332 that interacts with the discontinuity 320. Thereturning waves 333 from the discontinuity 320 may be detected by thesignal emitter 330, in the case of a transducer, or a separate detectingdevice. Different discontinuities 320 may each uniquely affect theemitted signal. That is, a change in material thickness or materialcomposition may affect the emitted signal differently from variationsalong a surface (e.g., a protrusion, recess, cavity, etc.). The detectedreturning waves 333 can be processed to determine if the detectedsignals are indicative of a juncture between two plates or some otherdiscontinuity. The FIG. 5B arrangement may be considered an activesystem because energy is emitted to detect the discontinuity 320.

In FIG. 5C, the mobile platform 100 includes a tactile detector 335 thatphysically contacts the surface 322 and detects characteristics such asa change in inclination, clearance, or roughness that are indicative ofthe discontinuity 320. In one embodiment, the tactile sensor 335 may“feel” the contour by using a ball wheel 336 pushed down by gravity, orusing a biasing member, to trace the surface 322. A sensor 337, such asa Hall sensor, inside a supporting vertical tube 338 may sense themovement up and down of a supporting shaft 339. Other tactile detectors335 may measure a deflection, bend, or other deformation in a member(not shown) contacting the surface 322.

In FIG. 5D, the mobile platform 100 includes an optical detector 340that optically scans the surface 322 and detects visual characteristicsthat are indicative of the discontinuity 320. In one embodiment, a lightsource 341, which may be positioned in one or more external enclosures(not shown), emits light 343 that illuminates the surface 322. Theoptical detector 340 can record the reflected light 347 for processingand analysis.

FIG. 5E illustrates another embodiment wherein the mobile platform 100includes an optical detector 340 that optically scans the surface 322and detects visual characteristics that are indicative ofdiscontinuities (not shown). In this embodiment, the optical detector340 and the light source 341 are positioned on one or more verticalfaces 345 of the mobile platform 100. The vertical face 345 may be thefront or the back of the mobile platform 100. It should be appreciatedthat any of the other sensors and detectors discussed may also bemounted on one or more vertical faces 345 or faces other than vertical(not shown). That is, the present disclosure is not limited to onlydownwardly directed sensing devices. Additionally, while described asconfigured for detecting discontinuities, the above-described sensorarrangements may be used to locate, identify, and characterize otherfeatures such as pumps, equipment, pillars, etc., for general steering,obstacle avoidance, or other purposes.

It should be noted that the discontinuity 320 may be detected bymeasuring any number of material or structural features; e.g., changesin wall thickness, material composition, roughness, density, color, etc.Numerous types of passive and active sensing devices may be used todetect discontinuities. Illustrative, but not exhaustive, sensingdevices include: devices using reflections of electromagnetic waves suchas LIDAR or other related laser-based sensor, a camera or other imagesensor, a radar sensor; devices that use reflections of mechanical wavessuch as an ultrasonic sensor and a sonic sensor; devices that detect achange in orientation relative to the gravity vector such as inertialmeasurement unit (IMU), accelerometers, gyroscopes, and inclinometer;devices that detect variances in speed, voltage, current, and/or powerusage within the propulsion system 400 (FIG. 2) caused by traversing adiscontinuity 320; tactile devices configured to “feel” thediscontinuity; and devices that detect changes in the transmission ofmagnetic fields such as a magnetic flux leakage sensor and an eddycurrent sensor.

Thus, it should be appreciated that the marker detector 306 may be anorientation sensor such as the inclinometer 328, a signal emitter 330that emits an energy wave 332, a tactile detector 335 that contacts asurface 322, and/or an optical detector 340 that optically scans asurface 322. However, the marker detector 306 may be any device that isconfigured to detect the presence of an active and/or passive marker.

FIGS. 6A, B illustrate a method by which the control unit 300 mayintelligently traverse an interior of a tank 10 using the navigationmodule 304 that detects discontinuities 320, which are shown in FIG. 6B.FIG. 6B is a top view of a tank bottom wall 18 that includesdiscontinuities 320 in the form of weld structures. Some discontinuities320 follow a grid-like pattern, such as weld lines formed byintersecting perpendicular lines. Other discontinuities 320 do notconform to a particular order or geometric pattern, such as the weldlines next to the wall 20.

Referring now to FIGS. 1, 2, 4 and 6A, the control unit 300 may includeone or more navigation algorithms that use the discontinuities 320 tosteer the mobile unit 100 in accordance with the FIG. 6A method. Step800 begins after the mobile platform 100 has been positioned in the tank10. The control unit 300 may initiate operations by executing anavigation algorithm that issues control signals 308 to the propulsionsystem 400. The propulsion system 400 may transmit information 313 tothe control unit 300 that relates to system operations (e.g.,confirmation of commands, system status, operating set points, etc.).The navigation algorithm may move the mobile platform 100 randomly oraccording to a preset initial course.

At step 802, the marker detector 306 passively or actively scans theinterior of the tank 10 for discontinuities 320. If the marker detector306 is a component of the task module 600, the control unit 312 maytransmit control signals 312 to the control the task module 600 and thetask module 600 may transmit information 311 representative of thedetected discontinuities 320. The discontinuities 320 may be structuralor augmented and be present in any of the walls of the tank 10 or otherstructures of the tank, such as the pillars 26 or equipment (e.g.,sump). As signals are received, the control unit 300 may analyze thesesignals to determine if a discontinuity for steering the mobile platform100 has been detected. At step 804, if such a discontinuity has beenfound, the control unit 300 accesses a map, which is a digital database(e.g., database 303 a (FIG. 4)). In some arrangements, data in the mapdatabase is referenced to estimate a position or orientation of themobile platform 100. In other arrangements, the control unit 300 createsthe map or updates the map, if pre-existing, to record the position orrelative position of the detected discontinuity and/or theposition/relative position of the mobile platform 100. In this instance,the relative position may include an element of the position such as adistance travelled from another feature, a heading taken from anotherfeature, and/or an orientation relative to another feature.

At step 806, the control unit 300 may set a course based on one or moredetected markers, which may be passive markers such as discontinuities.The course may be in parallel with, perpendicular to, or another headingrelative to the detected discontinuity or a feature identified by thedetected discontinuities, such as a corner. While following the setcourse, the mobile platform 100 may perform one or more of the assignedtasks using the task module 600, such as scanning the tank bottom wall18 for corrosion or other forms of damage. Also, one or more databases(e.g., 303 b (FIG. 4)) may be continually updated with the positions,relative positions, and/or orientations of the detected discontinuities.The control unit 300 may repeat steps 802 to 806 as desired. Optionally,the control unit 300 may utilize information in the map, e.g., thelocation of previously detected discontinuities, along with theinformation relating to the currently detected discontinuity todetermine a heading. A similar methodology may be used when detectingone or more active markers.

At step 808, the control unit 300 may determine that one or more presettermination criteria have been met. The termination criteria may bebased on completion of the assigned task(s). Termination criteria mayalso be based on a time duration (e.g., a maximum of thirty-six hours inthe tank 10), battery life (e.g., battery drained to ten percent ofcapacity), system health, operating condition, or another presetparameter. Upon determining that the termination criteria have beensatisfied, the control unit 300 may initiate a power down of the mobileplatform 100. Optionally, at step 810, the control unit 300 may instructthe mobile platform 100 to move to a predetermined retrieval location.

It should be appreciated the FIG. 6A method allows the mobile platform100 to traverse the interior of the tank 10 without any “real time” or“near real time” human input. That is, human interaction with the mobileplatform 100 may end after the mobile platform 100 is released insidethe tank 10. Thus, the mobile platform 100 may be considered intelligentin that information relating to the environment is autonomouslycollected and processed in order to methodically traverse the interiorof the tank 10. It should be understood that the described steps do notnecessarily have to occur in the order described. For example, step 802may occur before, simultaneously with, or after step 800. It is alsoemphasized that the FIG. 6A method is only one of numerous controlschemes that may be used to imbue the mobile platform 100 withintelligent control. Other control schemes are discussed in detaillater.

Referring to FIG. 7, there is shown one non-limiting embodiment of apropulsion system 400 according to the present disclosure. Thepropulsion system 400 may be configured to provide the mobile platform100 with multiple degrees of freedom of movement. That is, the mobileplatform 100 can change positions in the tank 10 (FIG. 1) by at leasttwo or more of types of movement. These movements include linearmovements such as surge (forward/backward), heave (up/down), and sway(left/right) and rotation movements about an axis such as pitch (lateralaxis), yaw (normal axis), and roll (longitudinal axis). The propulsionsystem 400 may include an electrically powered internal rotary powerdevice 402 and an external drive assembly 404. The rotary power device402 may include a suitable motor. A drive shaft 412 extends through theenclosure wall 220 via an opening 440 and physically connects theinternal rotary power device 402 to the external drive assembly 404. Aseal 414 disposed in the enclosure wall 220 surrounds the drive shaft412. The seal 414 may independently provide adequate sealing protectionagainst tank fluids leaking into the enclosure interior 208 (FIG. 3). Insome embodiments, a pressurizer 430 may release a pressurized gas thatmaintains or increases the pressure of the fluid in the enclosure 200(FIG. 3) to be the same as or greater than the pressure of the fluidoutside the enclosure 200 (FIG. 3); i.e., a neutral to a positivepressure differential. It should be understood that other types ofpropulsion systems may also be used.

Mobile platforms 100 of the present disclosure are not limited to anyparticular type or number of external drive assemblies. A mobileplatform 100 may utilize a single external drive 404 assembly or two ormore external drive assemblies 404. Also, the external drive assembly404 may include gearing 405 for driving one or more impetus members suchas wheels 450 as shown in FIG. 7B or tracks 442 as shown in FIG. 5A.Other arrangements may use propellers or impellers for impetus members.Thus, any structure that is capable of using the rotary power to providethe impetus for moving mobile platform 100 may be used. Herein, anystructure or body configured for such use may be referred to as animpetus member. In some embodiments, the impetus member(s) may includemagnetic elements or other device that enable the mobile platform 100 toclimb vertical walls or hang from ceilings.

Mobile platforms 100 of the present disclosure are also not limited tothe internal drive and external drive assembly configurations describedabove. FIG. 7 depicts an impetus member having a dedicated internalrotary power device 402. However, in variants, a propulsion system 400may include one internal rotary power device 402 that drives two or moreexternal drive assemblies 404. Thus, arrangements for the propulsionsystem 400 may or may not have a one-to-one correspondence between theinternal rotary power devices 402, and the external drive assemblies404.

Referring to FIG. 8, power for the subsystems of the mobile platform 100may be supplied by the power supply 500. The power supply 500 mayinclude a battery bank 502 housed within a suitable casing 504. In someembodiments, one power supply 500 energizes all of the subsystems. Inother embodiments, two or more separate power supplies 500 may be used.Additionally, electronic and computer-implemented controls for powerdischarge may be performed by suitable processing circuitry (not shown).Generally, the power supply 500 supplies power at a level to fullyenergize all subsystems of the mobile platform 100 because the mobileplatform 100 does not have an active line supplying power duringoperations. By “fully” energized, it is meant that that a subsystem issupplied with sufficient energy to execute all intended functions.

Referring to FIGS. 9A,B, there is shown one embodiment of a task module600 that may be carried by the mobile platform 100 to performinspections of a tank wall 16, 18, 20 (FIG. 1). The task module 600 mayinclude one or more instruments that collect information from which thethicknesses of sections or segments of the walls making up the tank maybe determined. In one embodiment, the task module 600 includes atransducer array 602 configured to direct acoustic signals throughwindows 232 out from the bottom 206 of the enclosure 200. The windows232 may be sealed with a material (not shown) such as a polymer that isconductive to acoustic energy. Thus, the windows 232 do not impair theliquid-tight nature of the enclosure 200. In one arrangement, thetransducer array 602 may include a plurality of sensors that emitsignals into the tank wall 16, 18, 20 (FIG. 1) and detect thereflections of these signals. Illustrative sensors include, but are notlimited to, sonic sensors, ultrasonic sensors, magnetic field and fluxdetectors. The detected signals may be digitized using appropriatecircuitry and transmitted to the control unit 300 (FIG. 2) via acommunication link 604. The control unit 300 (FIG. 2) can store theinformation in a suitable memory module for later retrieval. It shouldbe noted that the transducer array 602 may also be used to identifydiscontinuities for navigation/guidance purposes. The task module 600may be supported by a suitable base 230 (FIGS. 3B, C) fixed in theenclosure 200 (FIGS. 3B,C).

It should be understood that the task module 600 may also incorporateother devices for estimating the condition or state of one or morefeatures of the tank 10. The features may be one or more structuresmaking up the tank 10 or an ambient condition in the tank 10. Referringto FIGS. 2 and 5A-E, by way of non-limiting examples, the task module600 may include an orientation sensor such as the inclinometer 328, asignal emitter 330 that emits an energy wave 332, a tactile detector 335that contacts a surface 322, and/or an optical detector 340 thatoptically scans a surface 322. These instruments may provide informationrelating to the condition of the walls or of other structures of thetank 10 such as corrosion, damage, structural integrity, etc. The taskmodule 600 may also incorporate devices for the retrieval of materialsfrom the inside of the tank 10 or for the delivery of materials to theinside of the tank 10.

The mobile platform may optionally include other mechanisms to enableadditional functions. Other examples of such devices are described inconnection with FIGS. 10 and 11A-D below.

Referring to FIG. 10, there is shown a switch assembly 250 forcommunicating with the mobile platform 100 (FIG. 2). For example, theswitch assembly 250 may be used to shift between power states, activateor de-activate sub-systems, initiate pre-programmed instructions, etc.The switch assembly 250 is a non-momentary type that does not require apassage to the interior 208 of the enclosure 200. A “momentary switch”only engages while actuated. A “non-momentary switch” latches andremains in a set position. In one non-limiting embodiment, the switchassembly 250 may have a lever member 251 positioned on or near an outersurface of the enclosure 200. The lever member 251 may have an externalmagnetic element 252, or a magnetic material such as iron, and that ismoveable between two positions, e.g., an “off” position 254 and an “on”position 256 (shown in hidden lines). The movement may be a rotationand/or a translation. Sealed inside the enclosure 200 is a sensor 258that can detect a magnetic field such as a Hall effect type sensor or areed switch. Shifting the switch assembly 250 from the “off” position254 to the “on” position 256 causes the sensor 258 to transmit a signal260 to the control unit 300 (FIG. 2)). Other non-momentary switches mayutilize pressure activation or a command signal (e.g., acoustic wave).

Referring to FIGS. 1, 2, and 10, in one non-limiting method ofoperation, the switch assembly 250 is moved to the “on” position whilethe mobile platform 100 is outside of the tank 10 (FIG. 1). The signal260 received by the control unit 300 from the switch assembly 250commands the control unit 300 to shift from a no-power, low-power orsleep mode to a higher power consuming mode, such as a “start ofoperation” mode. The “start of operation” mode may begin with a systemcheck, the successful conclusion of which may be indicated by an audio,visual, mechanical (e.g., shock, vibration, impact, pressure, physicalmovement, etc.), or electromagnetic (EM) signal. Next, the control unit300 may start a preset duration for a quiet mode of, say thirty minutes.In the quiet mode, the control unit 300 remains functionally dormantwhile the mobile platform 100 is being positioned in the tank 10. At theend of the quiet mode, the control unit 300 may enter a period wherequiescence is monitored. For example, an on-board motion sensor, such asan accelerometer, may be used to detect whether or not the mobileplatform 100 is moving. If the mobile platform 100 has been determinedto be motionless for a preset duration, e.g., thirty minutes, then thecontrol unit 300 may commence operation, which may be the highest powerconsuming mode. It is emphasized that the described switch assembly andmethod for commencing operations is only one of various devices andmethods that may be used to bring the mobile platform 100 (FIG. 2) tooperational readiness.

Referring now to FIG. 11A, there is shown one non-limiting embodiment ofa retrieval module 700 that may be used to retrieve the mobile platform100 from the tank 10 at the conclusion of operations. As notedpreviously, the mobile platform 100 may be fully submerged, perhaps byseveral feet, within a liquid contained in the tank 10 (FIG. 1). Theretrieval module 700 may release a buoy that can float at or below theliquid surface to facilitate location and retrieval. In one embodiment,the retrieval module 700 includes a buoyant body 702 having an innercompartment 704 in which a tether 706 is stored. The body 702, whileshown as cylindrical, can be of any shape or size. The body 702 may beformed of one or more materials that enable the body 702 to be buoyantin the surrounding liquid. Optionally, the body 702 may be inflatablewith a gas. For example, the body 702 may be formed as an expandable bagor bladder that can increase in volume using pressurized gas. A handle708 or other suitable projection such as an eyelet may be fixed to anouter surface of the body 702. The body 702 may also include one or moremagnetic elements 710 disposed on a lower portion and in close proximityto the outer surface of the enclosure 200. In embodiments, a magneticsteel may also be suitable. Sealed inside the enclosure 200 may be oneor more electro-magnets 712. The electro-magnets 712 may be electricallyconnected to the control unit 300 (FIG. 2) and the power supply 500(FIG. 2) via one or more lines 214. The magnetic elements 710, theelectromagnets 712, and the control unit 300 form a latch assembly 715that uses a magnetic force for selectively releasing the buoyant body702.

During operation, the latch assembly 715 is in a locked position whereinthe electro-magnets 712 are kept energized so that a magnetic connectionis maintained with the magnetic elements 710. Thus, the buoyant body 702is fixed to the enclosure 200. At the appropriate time, the control unit300 shifts the latch assembly 715 to the released position whereinelectro-magnets 712 are de-energized by terminating electrical power,which eliminates the magnetic connection. The buoyant body 702 thenfloats to or near the surface of the liquid in the tank 10 (FIG. 1). Thetether 706 connects the body 702 to the mobile platform 100. Thus, themobile platform 100 may be retrieved by pulling on the tether 706 orusing the tether 706 as a guide to physically locate the submergedmobile platform 100. When the tether 706 is used as a retrieval carrier,then the tether 706 may use materials and construction that providesuitable loading capacity to support the mobile platform 100.

Referring now to FIG. 11B, there is shown in schematic form anothernon-limiting embodiment of a retrieval module 700 that may be used toretrieve the mobile platform 100 from the tank 10 at the conclusion ofoperations. In this embodiment, the retrieval module 700 includes abuoyant body 702, a handle or other similar manipulation member 708, andone or more electro-magnetically actuated latches 724. The latches 724may positively engage a lip 730 of the buoyant body 702 and thereby fixthe body 702 against the enclosure 200. The latches 724 may be shiftedbetween a locked and unlocked position using electromagnetic typeactuators 726. In the illustrated embodiment, the latches 724 slide awayfrom the lip 730 in the direction shown by arrows 728 when theelectromagnetic actuators 726 are energized. Other modes of movement orshifting may be used; e.g., rotational, pivoting, etc. Optionally, aswitch assembly 250 may be fixed to one of the latches 724. The switchassembly 250 may be similar to that shown in FIG. 10. In onearrangement, when the latches 724 are in the closed position as shown,the switch assembly 250 is in “on” position. When the latches 724 areslid to the open position to release the buoyant body 702, the switchassembly 250 shifts to the “off” position, shown in hidden lines. Itshould be noted that a latch assembly having one or more latches andelectromagnetic actuators may also be used in the FIG. 11A embodiment.

The retrieval module 700 of FIG. 11B uses a two-stage external tether736 that includes a relatively light first stage tether 738 and arelatively stronger second stage tether 740. The first stage tether 738may be connected by a flexible member 742, such as a wire, to the body702. The material of the first stage tether 738 is selected to be lightenough as to not impair the buoyancy of the body 702 but be strongenough to support the weight of the second stage tether 740 as thesecond stage tether 740 is unwound and retrieved. The material of thesecond stage tether 740 is selected to be strong enough to support theweight of the mobile platform 100 during retrieval. The second stagetether 740 may also be referred to as a retrieval carrier. Thus, eachtether 738, 740 may have different loading capacities (e.g., tensionloading). As a consequence, whereas a polymer cable may be suitable thefirst stage tether 738, a metal cable may be more appropriate for thesecond stage tether 740. However, any material-type may be used foreither stage tether 738, 740 as long as their respective loadingrequirements are satisfied.

The FIG. 11B also integrates the shutdown of the mobile platform 100into the operation of the retrieval module 700. Sealed inside theenclosure 200 may be one or more electro-magnets 726. Theelectro-magnets 726 may be electrically connected to the control unit300 and the power supply 500 via one or more lines 214. While the mobileplatform 100 is operating, the electro-magnets 726 maintain the latches724 in the locked position. Thus, the buoyant body 720 is fixed to theenclosure 200. At the appropriate time, electro-magnets 726 may bede-energized by terminating electrical power, which eliminates themagnetic connection. The buoyant body 702 then floats toward the surfaceof the liquid in the tank 10 (FIG. 1). At the same time, the latches 724move to the unlocked position, the switch assembly 250 shifts to the“off” position, which shuts down the mobile platform 100. Thereafter,the mobile platform 100 may be retrieved by first pulling on the firststage tether 738 to retrieve the second stage tether 740 and thenpulling up the submerged mobile platform 100 using the second stagetether 740. It should be noted that a switch assembly 250 may also beintegrated with the retrieval module of the FIG. 11A embodiment.

Referring now to FIGS. 11C-D, there are shown devices that may be usedto facilitate deployment and/or retrieval of a mobile platform 100. FIG.11C schematically illustrates a deployment assembly 760 that includes adock 762 connected to a carrier 764. The mobile platform 100 may connectto the dock 762 using a mechanical and/or magnetic coupling 763.Optionally, the deployment assembly 760 may include a signal emittingbeacon 766 that emits a wave 768, such as an electro-magnetic oracoustical wave. The carrier 764 may be a passive physical line, such asa cable, wire or rope. By “passive,” it is meant that the carrier 764does not convey signals, pressurized fluids, or power. The carrier 764has sufficient tensile strength to convey the deployment assembly 760and mobile platform 100 into the tank 10. In one mode of use, thedeployment assembly 760 and mobile platform 100 may be lowered into atank 10 together. Thereafter, the mobile platform 100 decouples from thedock 762 and moves freely, as shown in hidden lines. The deploymentassembly 760 may be extracted from or remain in the tank 10 duringoperations. If the deployment assembly 760 remains in the tank 10 duringoperations, the carrier 764 may provide a physical, passive connectionbetween the dock 762 and an object (not shown) inside or outside of thetank 10. Upon completion of operations, the mobile platform 100 mayreturn and re-connect to the dock 762 for retrieval or be retrieved inanother manner. In some embodiments, the carrier 764 may be used withoutthe dock 762 to deploy and/or retrieve the mobile platform 100. That is,the carrier 764 may be configured to function as a deployment carrierand/or a retrieval carrier.

If present, the beacon 766 may emit a signal that the mobile platform100 may use for navigation or other purposes. It should be understoodthat the beacon 766 is merely representative of any number of devicesthat may be carried by the dock 762. For instance, a control unit (notshown) may be carried by the dock 762 and communicate with the mobileplatform 100.

FIG. 11D schematically illustrates a passive carrier 780 that remainsconnected to the mobile platform 100 during operations in the tank 10.The passive carrier 780 may be a rope, wire, cable, or othertension-bearing member that may be used to move or simply locate themobile platform 100. As noted above, a passive carrier does notcommunicate any power, signals, or materials (e.g., pressurized gas) toor from the mobile platform 100. Rather, the carrier 780 may provide aphysical, passive connection to an object inside or outside of the tank10. Thus, the carrier 780 may act as a deployment and/or retrievalmechanism or a line that allows the mobile platform 100 to be located.

Referring now to FIGS. 12A-B, there is shown another embodiment of anintelligent mobile platform 100 according to the present disclosure.Similar to the embodiment of FIG. 2, the mobile platform 100 includes anenclosure 200, a control unit 300, a propulsion system 400, a powersupply 500, and a task module 600. The lid 204 of the enclosure 200 isshown only in FIG. 12B to better illustrate the interior 208 in FIG.12A. The details and variants of the enclosure 200, propulsion system400, power supply 500, and the task module 600 have been described indetail above. The FIG. 12A embodiment includes a non-momentary switch250 as described in connection with FIG. 10 and a retrieval module 700as described in connection with FIGS. 11A-B. An eyelet 240 may be fixedto the lid 204. The eyelet 240 may be any loop, hook, or other body towhich a lifting/handling device can be releasably connected. The controlunit 300 of the FIGS. 12A-B embodiment is discussed below.

Referring to FIG. 13, the control unit 300 of the FIGS. 12A-B mobileplatform includes a navigation module 304 having two or more distincttypes of sensing instruments. The first sensing instrument is a markerdetector 306 that detects discontinuities as described previously inconnection with FIGS. 4-5E. The second sensing instrument may be adynamic sensor 380 that estimates one or more navigation parameters. Asused herein, a navigation parameter characterizes an absolute and/or arelative position of the mobile platform 100 in a desired coordinatesystem (e.g., x/y space, polar coordinate defined space) and/ororientation (e.g., direction faced, inclination, etc.). For example, thedynamic sensor 380 may estimate a parameter such as a distancetravelled, a degree of rotation, acceleration, tilt, and/or relativechanges in the direction of movement. While referred to in the singular,it should be understood that the dynamic sensor 380 may comprise a suiteof two or more discrete and different sensors, each of which providedifferent information. Suitable dynamic sensors include, but are notlimited to, odometers, RPM sensors, inclinometers, gyroscopes, andaccelerometers. Still other dynamic sensors may sense operatingparameters of motors, transmissions, and motor controllers (not shown).The information from a dynamic sensor 380 may be used to steer in adesired direction, reduce errant motion of the mobile platform 100(FIGS. 12A-B), steer past obstacles, and/or identify locations ofinterest (e.g., a retrieval point).

Some of the uses for the information provided by the dynamic sensor 380may be illustrated with reference to FIG. 14, which shows a portion of atank bottom wall 18 formed of steel plates, an obstacle such as a pillar26, and a retrieval point 382. Referring to FIGS. 12A-B and 13, duringoperation, the mobile platform 100 may follow a path having a leg 384.The mobile platform 100 may have started on the leg 384 upon the markerdetector 306 detecting a discontinuity 320. Thereafter, the dynamicsensor 380 may provide information that can be used to issue steeringinstructions to steer the mobile platform 100 along the leg 384. Thus,for instance, the dynamic sensor 380 can detect if the mobile unit 100has drifted to the left or right from a desired heading and quantify theamount of variance from the desired heading. Corrective steeringcommands can be issued based on this information.

During operation, the mobile platform 100 may encounter a number ofobstacles. One common obstacle is a pillar 26. Other obstacles includesumps, walls, bracing structures, debris, joints, etc. As notedpreviously, some are known whereas others have entered the tank 10unintentionally. The mobile platform 100 may be programmed to handlesuch obstructions using a variety of techniques. For instance, uponencountering the obstacle 26, the steering algorithm may direct themobile platform 100 to incrementally change direction to maneuver aroundthe obstacle 26 until the mobile platform 100 has returned to a headingof the prior leg 384. Thereafter, the mobile platform 100 begins thenext leg 386.

The return to the heading of the prior leg 384 is enabled by theinformation provided by the dynamic sensor 380. For instance, thedynamic sensor 380 can determine the degree of rotation and the distancetravelled during the maneuvering. Additionally, when preset criteria aremet, such as the conclusion of the task, the dynamic sensor 380 canprovide information for steering the mobile platform 100 to theretrieval point 382. For instance, the dynamic sensor 380 can determinethe degree of rotation required to head toward the retrieval point 382and the distance travelled while heading to the retrieval point 382.

It should be understood that the mobile platform 100 does notnecessarily carry all the above-described features and components withina single enclosure. Rather, in some embodiments, the above-describedcomponents may be dispersed into two or more separate enclosures thatmay be physically attached to one another. For instance, in someembodiments, an enclosure having only a power supply 500, a propulsionsystem 400, and task module 600 are in one mobile enclosure, and theremainder of the components, such as the control unit 300, are in aseparate enclosure.

An illustrative mode of use of the mobile platform of FIGS. 12A-B willbe discussed with reference to FIGS. 15 and 16A, B. FIG. 15 is a flowchart that identifies the several steps by which the mobile platform 100is used to perform one or more functions in a tank 10. FIG. 16Aschematically illustrates the mobile platform 100 during insertion intoa tank 10 and during operation and FIG. 16B schematically illustratesthe mobile platform 100 ready for retrieval after operation. While notalways the case, the tank 10 is shown filled with liquid 12, such as ahydrocarbon, at a level that fully submerges the mobile platform 100.Above the liquid body 12 is a gaseous body 14, which may also be ahydrocarbon. Other substances, such as dirt and debris, may also be inthe tank 10.

At step 850, the mobile platform 100 is activated while outside of thetank 10, such as by using the switch 250, to enter a pre-operation mode.At this time, the control unit 300 may initiate one or more diagnosticsweeps and provide an indication to a work crew that on-board systemsare functional. Thereafter, the control unit 300 may enter a quiet modewhile the work crew inserts the mobile platform 100 into the tank viathe hatch 24 at step 852. The mobile platform 100, shown in hidden linesin FIG. 16A, may be lowered into the tank using a suitable deploymentcarrier 50 and bracing structure (not shown). The deployment carrier maybe a non-rigid carrier such as tether, which may comprise a rope, cable,chain, etc. In other embodiments, the deployment carrier may be rigid,such as a pipe, pole, or tube. At step 854, after the mobile platform100 rests on the tank bottom wall 18, the deployment carrier 50 isdecoupled and retrieved and the hatch 24 may be closed.

At step 856, the mobile platform 100 may execute a “countdown” phaseduring which the mobile platform 100 monitors one or more inputs, suchas time and/or movement, to determine whether to enter a fulloperational mode.

Upon deciding to enter full operational mode, the control unit 300 mayenergize the necessary subsystems and begin execution of thepre-assigned task(s). It should be noted that the mobile platform 100has not required a communication link with operators, human orotherwise, that are outside of the tank 10. Therefore, all decisions tobe made during operations may be done by the control unit 300 usingpre-programmed instructions and by obtaining relevant information, i.e.,intelligently. However, in some variants, human or machines positionedexternal to the tank may interact with the mobile platform 100. Forexample, striking the wall of the tank 10 may be used to impart anacoustic command signal to the mobile platform 100 (e.g., “turn on,”“turn off,” “return to retrieval location,” “switch operating modes,”“transmit a signal,” etc.).

Steering the mobile platform 100, at step 858, may include locating oneor more discontinuities using the marker detector 306, as described inreference to FIGS. 4-6A, and estimating one or more navigationparameters using dynamic sensors as described in connection with FIGS.13-14. The control unit 300 processes this information to traverse thetank interior 22 using a predetermined methodology. It should be notedthat the mobile platform 100 has no active physical connection afterdeployment as shown in FIGS. 16A,B. Specifically, no energy (e.g.,electricity), data signals, or materials such as pressurized gases arecommunicated to the mobile platform 100 via a wire, cord, cable, pole,tube, pipe, or any other rigid or non-rigid conveyance carrier from alocation external to the tank 10. Thus, as used herein, an “active” lineor carrier is one that communicates or transmits power, materials, ordata signals while the mobile platform 100 is in the tank 10. As notedabove, the mobile platform 100 may have a passive carrier as discussedin connection with FIGS. 11C-D. A “passive” line or carrier is one thatdoes not communicate or transmit power, materials, or data signals whilethe mobile platform 100 is in the tank 10.

Step 860, which may be implemented for operations involving tankinspections, may be performed concurrently with step 858. Using thesensing device as described in connection with FIG. 13, the mobileplatform 100 scans one or more walls of the tank 10 using an inspectionmodule such as the task module 600 shown in FIGS. 9A-B. The task module600 and the control unit 300 can collect, organize, and process theinformation required to generate a database of the wall thicknesses forthe scanned areas of the tank 10. The database may include thethicknesses of all sections of the tank bottom wall 18 or thicknesses ofjust the locations/sections that are “out of norm” (i.e., different froma specified value or range). The walls inspected typically include thetank bottom wall 18. It should be noted that for inspections, thesensing device used to inspect the walls of the tank 10, such asultrasonic sensors, may also be used as a marker detector 306.

In one non-limiting method, the mobile platform 100 performs thescanning activity by first locating the edges, or sides, that define aperimeter of a plate. For instance, the mobile platform 100 may firstlocate a corner of the plate by tracing an edge until another edge isfound, which identifies the corner. Tracing may be performed any numberof ways including following a reversing path (e.g., zigzag) along adetected edge. Next, the mobile platform 100 may steer parallel to oneof the edges of that corner to locate the opposite corner. Locating theother corner then establishes the position of two parallel edges and oneperpendicular edge of the plate. The mobile platform 100 may moveincrementally along the parallel edges to locate the remaining cornersof the plate. Thereafter, the mobile platform 100 may initiate a wallthickness scan of that plate. Once complete, the process can be repeatedfor another plate. In another non-limiting method, the mobile platform100 may first identify the edges of all the plates making up the tankbottom wall 18 of the tank 10. Afterwards, the mobile platform 100 canscan each of the plates. It should be noted that the multiple degrees offreedom along which the propulsion system 100 may move the mobileplatform 100 enables efficient execution of the above task, as well asother tasks.

At step 862, the mobile platform 100 begins the termination ofoperations. The termination may be triggered using any number ofconditions. These conditions may be related to quality and/or quantityof information obtained during inspections, completion of assignedtasks, remaining power levels, operational considerations such aspossible malfunctions, etc. One illustrative termination sequence mayinclude navigating to a predetermined retrieval location. This locationmay be below the hatch 24. Alternatively, if the mobile platform 100 hasmagnetic type external drive units, the mobile platform 100 may drive toa location proximate to the hatch 24. The magnetic type external driveunits (not shown) will enable the mobile platform 100 hang effectivelyupside-down from the top wall 16. Still other sequences may includesimply remaining in place and transmitting a signal that identifies thelocation of the mobile platform 100. The mobile platform 100 may beretrieved by hooking or otherwise connecting the mobile platform 100 toa suitable carrier, e.g., the deployment carrier 50. Thus, thedeployment carrier 50 may be also be used to retrieve the mobileplatform 100. The mobile platform 100 may also be retrieved by using aseparate retrieval mobile platform (e.g., deployment assembly 760 ofFIG. 11C) that can connect, to the mobile platform 100.

Step 864 may be used for a mobile platform that includes a retrievalmodule 700, such as that shown in FIGS. 11A-B. After moving to aretrieval location or staying in place, the mobile platform 100 releasesthe buoyant body 702. The buoyant body 702 floats to the surface of theliquid body or to a depth below the surface. Optionally, the buoyantbody 702 may emit a signal, fluoresce, and/or be illuminated. Finally,the mobile platform 100 may power down all subsystems, except any deviceon the buoyant body 702 that emits a signal. At step 866, the work crewcan extract the mobile platform 100 by connecting a retrieval carrier,such as a cable or pole, to the buoyant body 702 or other part of themobile platform 100. Alternatively, the mobile platform 100 may beretrieved by using a released tether as discussed in connection withFIGS. 11A, B.

The total “power down” or shut down of the mobile platform 100 at step864 may be initiated by the control unit 300. Alternatively, a retrievalmodule 700 as shown in FIG. 11B may be used to simultaneously releasethe retrieval body 702 and shut down the mobile platform 100. By “powerdown” or “shut down,” it is meant that the mobile platform 100 is in astate where no power is communicated to any sub-system and that nosub-system is consuming power or that no sub-system is consuming powerat a level that could potentially generate a spark.

In some embodiments, one or more elements or components of the mobileplatform 100 may remain in the tank 10 after retrieval. For example, themobile platform 100 may deposit an object that functions as an active orpassive marker to identify a retrieval point. The object left behind mayalso be a spent task module, a remnant of a deployment or retrievalcarrier, or other component that does not require retrieval.

Among the many advantages of the teachings of the present disclosure, atleast the following should be noted. One is that human presence was notrequired either inside or outside the tank 10 in order to operate themobile platform 100. Another advantage is that the mobile platform 100performed the inspection while the tank 10 contained liquids. Thus, thetanks themselves can continue to be used as normal without servicedisruptions. Still another advantage is that the tank 10 is sealed bythe hatch 24 during operation, which prevents the energetic substance 14from escaping into the surrounding environment. Thus, a spark occurringexternal to the tank 10, e.g., near the hatch 24, cannot ignite theenergetic substance 12, 14 inside the tank 10.

Referring to FIGS. 16A and B, it should be appreciated that embodimentsof the present disclosure that use ultrasonic sensing devices willoperate with better resolution because the mobile platform 100 issubmerged such that a liquid body extends between the mobile platform100 and one or more surfaces of the tank 10. The liquid body between theultrasonic sensors and a wall of the tank provides a highly efficientwave transmitting medium through which acoustic energy can betransmitted. Notably, such a liquid body or layer is not present wheninspections are performed by human personnel in air. Additionally, theability of the mobile platform 100 to operate while fully submerged canalso enable additional activities. For example, the mobile platform 100may utilize acoustic receivers to detect sounds associated with leakingfluid. For acoustic detection, the mobile platform 100 may enter asemi-quiet mode wherein movement is halted and any subsystems thatgenerate noise are shut down. In this semi-quiet mode, the acousticreceivers monitor the surrounding liquid body for acoustic signalscaused by fluid leaking out of the tank 10.

It should be appreciated that embodiments of the present disclosure thatuse the previously-described combinations of size and weightrestrictions may facilitate the handling and deployment of the mobileplatform 100 while also reducing the risk of damage to the tank in whicha task is performed.

While step 860 of the FIG. 15 method pertained to scanning walls of thetank 10 to determine thicknesses, it should be understood that the FIG.15 method may also be used to execute tasks related and unrelated toinspections. For example, other inspection methods such as visual scanscan be performed. For example, cameras may be used to collect visualimages of the tank walls such as the sides 20 and/or bottom 18.

The above-described systems and related methods used discontinuitiesassociated with the tank 10 (FIG. 1) as navigation markers, or simply‘markers,’ to control movement. The welds and plate overlapsrepresenting these discontinuities were formed while mating of steelpanels and thus may be considered structural elements of the tank 10.Thus, the above-described embodiments may be considered to intelligentlytraverse an interior of a tank 10 using structural markers. However,other embodiments of the present disclosure may utilize other types ofmarkers.

Referring now to FIG. 17, there are shown several types of markers thatmay be used to control the movement of the mobile platform 100 in thetank 10. By interacting with these markers, the control unit 300 (FIG.2) acquires an awareness of the location and/or orientation of themobile platform 100 relative to a given location in the tank 10.

A structural marker such as a discontinuity may be considered a passivemarker. By passive, it is meant that the marker is inert and does notoriginate a signal detected by the mobile platform 100. Another type ofmarker is energy emitting objects 902 a,b,c,d or ‘active markers,’ thatemit a magnetic, electromagnetic, acoustic, and/or optical signal.Active markers may be positioned inside and/or outside of the tank 10.For example, FIG. 17 depicts internal active markers 902 a,b andexternal active markers 902 c,d. Active markers may be utilized in avariety of methodologies. For example, a central internal active markercan be using by the mobile platform 100 as a homing beacon to identify aparticular location in the tank 10. Two or more spaced apart activemarkers may be used by the mobile platform 100 to locate itself and/or adirection within the tank 10.

In some embodiments, a marker is not rigidly fixed to the tank 10. Forexample, a marker 910 may float in a liquid body 12. The marker 910 mayfloat at the surface or be submerged at a selected depth below thesurface. Optionally, a tether 912 may connect the marker 910 to the tank10. The marker 910 may be active; e.g., transmit an energy signal suchas an acoustic wave. The marker 910 may also be passive; e.g., hang at adepth low enough as to allow contact with the mobile platform 100.

FIGS. 18A-B are flow charts of various guidance and navigationmethodologies that may use the above-described markers.

Referring to FIGS. 12A-B, 13, 17 and FIG. 18A, the control unit 300processes signals from active markers in order to generate commandsignals to operate the mobile platform 100. For example, at step 1100,the marker detector 306 may detect distinct signals emitted by aplurality of internal and/or external markers 902 a-d. At step 1102, thecontrol unit 300 may process the signals to estimate a current positionof mobile platform 100. Optionally, the control unit 300 may also usepre-programmed information such as the dimensions of the tank 10,relative locations of the active markers 902 a-d, as well as navigationparameters such as real-time information pertaining to orientation anddirection of movement obtained by dynamic sensors 380. At step 1104, thecontrol unit 300 issues a command signal to a subsystem such as apropulsion system 400 or the task module 600.

Referring still to FIGS. 12A-B, 13, and 17, in the FIG. 18A and FIG. 18Bmethods, the control unit 300 may have one or more memory modules 390,392. The memory module 390 stores information collected duringoperation. This information may be dynamically updated and includeinformation such as position of markers and currentposition/heading/orientation of the mobile platform 100. The memorymodule 390 may also store measured data indicative of the thickness ofwalls 16, 18, 20 of the tank 10. The memory module 392 may includepreprogrammed data that may be accessed while the mobile platform 100 isoperating. The preprogrammed data may be a digital representation (ormap) of a discontinuity pattern of one or more walls of the tank 10. Thediscontinuity may be the weld/overlap pattern of one or more walls 26,18, 20 of the tank 10. This information may have been obtained during aprevious operation in the tank. At step 1200, the marker detector 306may detect the discontinuity and generate responsive signals. At step1202, the control unit 300 may process the marker detector signals alongwith the information in the stored map to estimate a current positionand/or orientation of mobile platform 100. At step 1204, the controlunit 300 issues a command signal to a subsystem such as a propulsionsystem 400 or a task module 600.

Other navigation and guidance schemes may define a point and a line,such as an edge leading to a tank wall or by any two points. A mobileplatform 100 using such a scheme may have a control unit 300 programmedto estimate distances travelled using “dead reckoning” (e.g., bycounting wheel revolutions). Suitable sensors in the propulsion system400 may be used to sense when progress has been impeded by an obstacle(e.g., power variance) and/or travel reasonably straight withoutexternal references (e.g., RPM sensors on wheels, drive shaft, rotor, orother rotating element of the propulsion system). Optionally, aninternal navigation unit may be used to supplement navigation. Thecontrol unit 300 may be programmed to generate a “map” and proceedmethodically through the tank 10 by referencing the map and performingthe dead reckoning. The map, and any information gathered such as wallthickness data, may be correlated with the actual layout of the tankusing common pattern mapping techniques.

Still another navigation method may not use sense/detect markers or useinertial navigation units. Instead, the mobile platform 100 may beprogrammed to traverse the tank 10 and take pre-assigned actions whenencountering obstacles (e.g., turn until travel is unimpeded). Anyinformation gathered, such as wall thickness data, may be correlatedwith the actual layout of the tank using common pattern mappingtechniques.

The methodologies discussed above are not mutually exclusive. That is,portions of each of the described methods may be blended or separatemethodologies may be used concurrently. Some navigating methods involvegenerating a ‘map’ while performing one or more assigned functions.Other methods involve using a previously generated map in order tonavigate to one or more predetermined locations.

From the above, it should be appreciated that what has been disclosedincludes, in part, an apparatus for performing a selected task in a tankat least partially filled with an energetic substance. The apparatus mayinclude an inherently safe mobile platform that comprises at least onecontrol unit, at least one marker detector, at least one propulsionsystem, at least one power supply, and at least one inherently safeenclosure.

The at least one inherently safe enclosure is configured to prevent aspark occurring inside the at least one inherently safe enclosure frompassing to an exterior of the at least one inherently safe enclosure,the spark being capable of igniting the energetic substance. Allspark-generating components of the mobile platform are positioned insidethe at least one inherently safe enclosure.

The at least one marker detector is configured to detect at least onemarker associated with the tank. The at least one control unit isconfigured to generate at least one control signal based on the at leastone detected marker. The propulsion system moves the mobile platform inresponse to the at least one generated control signal. The propulsionsystem has a rotary power device positioned inside the at least oneinherently safe enclosure that supplies power to a drive assemblypositioned outside the at least one inherently safe enclosure. The powersupply energizes at least the at least one marker detector, the at leastone control unit, and the at least one rotary power device. No activephysical carrier connects the mobile platform to an object exterior ofthe tank while the mobile platform is in the tank.

Variants of the mobile platform may include arrangements wherein: the atleast one inherently safe enclosure is configured to not exhibit plasticdeformation that forms a path allowing a spark occurring inside the atleast one inherently safe enclosure from passing to an exterior of theat least one inherently safe enclosure after an interior of the at leastone inherently safe enclosure is subjected to at least three andone-half bar for at least ten seconds; the mobile platform is configuredto have at least two different degrees of freedom in the tank and tomove along the at least two different degrees of freedom using thepropulsion system; the mobile platform weighs less than 10,000 pounds(4,536 kg); the at least one control unit is programmed to determine aheading for the mobile platform based on the at least one detectedmarker, the heading being used to generate the at least one controlsignal; there are no physical carriers connecting the mobile platform toan object outside the tank; and/or the at least one power supplysupplies sufficient power to fully energize at least the at least onecontrol unit, the at least one marker detector, and the at least onepropulsion system. Also, in variants, the apparatus may include apassive carrier connected to the mobile platform while the mobileplatform moves in the tank.

In certain applications, the energetic substance is a liquid thatcontacts the mobile platform and an interior surface of the tank to forma wave transmitting medium. In such applications, the mobile platform isconfigured to transmit a wave and detect a reflection of the transmittedwave. The mobile platform can store information representative of thedetected reflection in a memory module.

Further, while the above-described embodiments of the mobile platform100 do not use a physical umbilical to receive power and/or communicatedata, it is within the scope of the present disclosure that a mobileplatform 100 may incorporate a carrier. The carrier may be a signalconveying media, e.g., a conducting cable or simply a cable that mayeffectively “leash” the mobile platform 100 to another object.

Referring to FIG. 1, it should be noted that structures for storingenergetic substances (12, 14), such as the tank 10, may be constructedin a manner that can hinder the deployment into and retrieval out of aninterior 22 of the tank 10. For example, access to the interior 22 mayonly be available through the hatch 24, which is positioned on the topwall 16. In many instances, access to objects in the interior 22 islimited to the zone or area in the immediate vicinity of the hatch 24.Limitations in the ability to detect the presence of an object, toidentify the object, and/or manually reach and contact the objectgenerally define such a zone or area. For instance, objects locatedimmediately adjacent to the vertical wall 20 may be undetectable topersonnel and not physically accessible without expending considerableeffort and employing relatively complex lifting and handling equipment.Moreover, the interior 22 may contain energetic substances (12, 14),which may be non-conductive, that may require additional restrictions tothe retrieval activity. As noted above, some classes of hydrocarbonliquids and gases are non-conductive. However, the teachings of thepresent disclosure may be readily applied to environments whereinenergetic and/or non-conductive substances are not present. Certainteachings of the present disclosure are directed to facilitatingretrieval of mobile platforms deployed in such environments.

Exemplary retrieval devices and related methods have already beendiscussed in connection with FIGS. 11A-D, 15, and 16B. Referring now toFIG. 19, there is schematically illustrated another non-limitingembodiment of the retrieval module 700 configured and implemented tosimplify locating and retrieving the mobile platform 100 from inside thetank 10.

For simplicity, the mobile platform 100 to be retrieved may beconfigured to include an enclosure 200, a control unit 300, a propulsionsystem 400, and a power supply 500. These components and sub-systemshave been already discussed above and will not be described in furtherdetail. It is emphasized that the configuration of these components andsub-systems are not limited to any particular previously describedembodiment. For example, the enclosure 200 need not be inherently safe.Moreover, two or more enclosures may form the enclosure 200, with eachof these separate enclosures acting as housing structures for differentcomponents. Further, optionally, the mobile platform 100 may be used inconjunction with a carrier 1002, which may be a passive or activecarrier. Such carriers have already been described and will not bedescribed in further detail.

The mobile platform may include a retrieval module 700 disposed at leastpartially on the enclosure 200. That is, the parts making up theretrieval module 700 may be internal and/or external to the enclosure200. Also, some parts may be embedded in a wall or body of the enclosure200. In one arrangement, the retrieval module may include a buoyant body702, a primary tether 1100, and a secondary tether 1102. The buoyantbody 702 is similar to that previously described. The primary tether1100 may be the same as the tether 738 of FIG. 11B.

In one arrangement, the primary tether 1100 and the secondary tether1102 are directly connected to one another, the primary tether 1100directly connects to the buoyant body 702, and the secondary tether 1102directly connects to the enclosure 200. An example of this configurationis illustrated in FIG. 11B, wherein the primary tether 1100 is formed bythe first stage tether 738 and the flexible member 742 and the secondarytether 1102 is formed by the second stage tether 740. It should be notedthat in this arrangement while the first stage tether 738 and 742 isshown as attached to the enclosure 200, the attachment is not onethrough which a force, such as tension, is intended to be transmittedduring retrieval of the mobile platform 100. Thus, as used herein, theterm “connection” refers to a functional engagement wherein there is acommunication of force (e.g., tension) or signals (i.e., power or data)between two or more locations as opposed to merely holding one bodystationary relative to another body.

In the FIG. 11B arrangement, the primary tether 1100 is indirectlyconnected to the enclosure 200 via the secondary tether 1102 and thesecondary tether 1102 is indirectly connected to the buoyant body 702via the primary tether 1100. By “indirect” connection, it is meant thatphysical engagement occurs through an intervening and functionallydistinct device or component.

Referring now to FIG. 20A, in another arrangement, the primary tether1100 and the secondary tether are both directly connected to the buoyantbody 702 and to the enclosure 200. It should be noted that the directconnection may include one or more elements specifically configured toform a connection, such as a chain, cable, or buckle. For instance, aportion of the secondary tether 1102 may be used to connect the primarytether 1100 to the buoyant body 702. A cavity, reel, or spool (notshown) inside or outside the buoyant body 702 may be used to store alength of the secondary tether 1102.

In the FIG. 20A arrangement, the primary tether 1100 is configured torelease the secondary tether 1102 by severing in some manner. Forinstance, the connection between the primary tether 1100 and theenclosure 200 can be broken by using a suitable breaking force or bytransmitting a signal. FIG. 20A shows the retrieval module 700 after thebuoyant body 702 has been released and rises toward a surface 1116 ofthe non-conductive, liquid energetic substance 12. The primary tether1100 connects the buoyant body 702 to the enclosure 200, while thesecondary tether 1102 is not under tension at a magnitude occurringduring the retrieval of the mobile platform 100. FIG. 20B shows theretrieval module 700 of FIG. 20A after the primary tether 1100 has beendisconnected from the enclosure 200 and the buoyant body 702 has beenextracted from the non-conductive, liquid energetic substance 12. Inalternate embodiments, the primary tether 1100 could decouple from onlythe buoyant member 702 or decouple from both the enclosure 200 and thebuoyant member 702. The primary tether 1100 may also sever at anintermediate location thereby releasing the buoyant member 702 from theenclosure 200 while having a severed portion connected to both. Now, thesecondary tether 1102 can act as a load bearing retrieval member forpulling up the mobile platform 200 toward the surface 1116 of thenon-conductive, liquid energetic substance 12.

Referring to FIG. 20C, there is shown another arrangement wherein theprimary tether 1100 is housed within the buoyant body 702. Whenactivated, the buoyant body 702 rises toward a surface 1116 of thenon-conductive, liquid energetic substance 12. As the buoyant body 702rises, the primary tether 1100 unspools, falls, or otherwise exits thebuoyant body 702.

While illustrated as single, unitary bodies, it should be understoodthat the buoyant body 702, the primary tether 1100, and the secondarytether 1102, may be formed of two or more separate portions, sections,or segments.

FIG. 21 illustrates a non-limiting embodiment of a retrieval method 1200according to the present disclosure. Referring to FIGS. 19 and 20A,B,the method 1200 may be of particular use when the tank 10 is at leastpartially filled with a non-conductive, energetic substance 12, 14. Atstep 1202, the mobile platform 100 may be configured as shown in FIG.19. However, the method 1200 may be used to retrieve other devices notdescribed in the present disclosure. At step 1204, personnel maypredetermine the buoyant body retrieval zone 1104 within the tank 10. Itshould be noted that the hatch 24 permits relatively easy access tocertain interior areas of the tank 100 directly below the hatch 24.However, because the hatch 24 is much smaller than the top 20, limitsaccess to areas closer to the vertical wall 20. Thus, the buoyant bodyretrieval zone 1104 may be based on the limitation in lifting, handling,and access associated with performing retrievals through the hatch 24.

At step 1206, the mobile platform 100 is lowered into the tank 10 usinga deployment carrier 50 (FIG. 16A). Other embodiments may use thedeployment carriers 764 or 780 (FIGS. 11C, 11D, respectively). At step1208, the enclosure 200 is submerged in the non-conductive, liquidenergetic substance 12. If two or more separate enclosures are present,then only one of those separate enclosure needs be submerged. Moreover,the enclosure 200 does not have be fully submerged; i.e., a partiallysubmerged state may be suitable in certain instances. At step 1209, themobile platform 100 may be moved by the propulsion system 400 to performone or more tasks in the tank 10.

At step 1210, which may be at or near the conclusion of operations, thebuoyant body 702 is released from the enclosure 200. It should be notedthat the buoyant body 702 and the primary tether 1100 are stillconnected to the enclosure 200 by the secondary tether 1102. The step1212, positioning of the released buoyant body 702 occurs within thebuoyant body retrieval zone—1106 by using the at least one primarytether 1100. At step 1214, retrieving the primary tether 1100 isperformed by using the buoyant body 702. For example, a retrieval member1110 may be inserted into the tank 10 through the hatch 24 to capturethe buoyant body 702. The retrieval member 1110 may be a pole, hook,lasso, net, rod or other elongated member. At step 1216, the primarytether 1100 may be used to release the secondary tether 1102. Forinstance, the primary tether 1100 may be used to transmit a force orsignal to the secondary tether 1102. Suitable forces or signals may betension, torsion, vibration, etc. At step 1218, the secondary tether1102 is used to retrieve the mobile platform 100 from inside the tank 10to outside the tank 10. The retrieval member 1110 may be insertedthrough the hatch 24 to retrieve the buoyant body 702, the primarytether 1100, and/or the secondary tether 1102. It should be noted thatother devices such as the primary tether 1100 and/or additional cables,wires, or other retrieval members may be used in conjunction with thesecondary tether 1102 to retrieve the mobile platform 100.

In embodiments, the primary tether 1102 may be configured to positionthe buoyant body 702 in the buoyant body retrieval zone 1104 byestimating a height of the non-conductive, liquid energetic substance 12above the mobile platform 100 inside the tank 10 and selecting a lengthof the primary tether 1100 based, at least in part, on the estimatedheight of the non-conductive, liquid energetic substance 12 above themobile platform 100 inside the tank 10. In some methods, the length ofthe primary tether 1100 is also selected using, at least in part, adistance between a retrieval location—1112 of the mobile platform 100and a wall 20 of the tank 10. In other methods, the length of theprimary tether 1110 is less than the square root of the sum of thesquare of the estimated height of the non-conductive, liquid energeticsubstance 12 above the mobile platform 100 inside the tank 10 and thesquare of a distance from the retrieval location 1112 of the mobileplatform 100 to a farthest point 1114 on the wall 20 of the tank 10 at alevel of the retrieval location 1112.

As discussed previously in connection with FIG. 19, the primary tether1100 may be used to release the secondary tether 1102. In onearrangement, the primary tether 1100 is configured to release thesecondary tether 1102 in response to an applied predetermined releasingforce. The releasing force may be selected to actuate a lever, break afrangible element, overcome frictional force, overcome a pre-tension inan object, bend, twist, or otherwise deform an object, overcome storedtension or spring force, or otherwise decouple the secondary tether 1102from a suitable retaining mechanism. During retrieval, applying a forcethat is at least as great as the predetermined releasing force to theprimary tether 1100 releases the secondary tether 1102. In onenon-limiting method, the predetermined releasing force is greater than anet buoyancy of the buoyant body 702 in the non-conductive, liquidenergetic substance 12 and less than a net downward force of the mobileplatform 100 in the non-conductive, liquid energetic substance 12.

Additional variants of the method 1200 include sizing the secondarytether to be at least long enough to traverse a distance between themobile platform 100 and a location proximate to a top wall 16 of thetank 100 and selecting a combined length of the primary tether 1100 andthe secondary tether 1102 is at least long enough to traverse a distancebetween the mobile platform 100 and a location proximate to a top wall16 of the tank 100. One skilled in the art would understand that what is“proximate” will depend on a position of the buoyant body 702 that isclose enough for personnel to reach and retrieve the buoyant body 702 orprimary tether 1100 from the hatch 24.

In some applications, the secondary tether 1102 is used to pull themobile platform 100 either partially or fully out of the tank 10. Forexample, the secondary tether 1102 may be used to pull up and supportthe mobile platform 100 at a surface 1116 of the non-conductive, liquidenergetic substance 12. Alternatively, the secondary tether 1102 may beused to lift the mobile platform 100 out of the non-conductive, liquidenergetic substance 12. In situations such as when a floating roof ispresent, the length of the primary tether 1100 may be selected tomaintain a predetermined gap between the buoyant body 702 and a top wall16 of the tank 10.

Referring to FIGS. 1 and 2, in certain situations, it may be desirableto reduce a voltage differential between the mobile platform 100 and thetank 10 and/or other surrounding electrically conductive structuresbefore completing retrieval of the mobile platform 100. Such a voltagedifferential may arise from an accumulation of electrical charge on themobile platform 100 due to relative motion between the mobile platform100 and contact with an adjacent surface and/or the operation ofconsumers of electrical energy onboard the mobile platform 100. Theadjacent surface may be a surface defining a wall 16, 18, 20 of a tank10, a pillar 26 of a tank 10, and/or the non-conductive, liquidenergetic substance 12. Exemplary electrical power consumers include,but are not limited to, the control unit 300, the marker detector 306(FIG. 4), the dynamic sensor 380 (FIG. 13), the propulsion system 400,and the task module 600 (FIG. 2). The type and number of electricalpower consumers will depend on the particular configuration of themobile platform 100. For simplicity, the term “on” will be used hereinto describe an electrical charge accumulation “on” and “in” the mobileplatform 100.

Further, while partially or completely submerged in the non-conductive,liquid energetic substance 12, the mobile platform 100 may beelectrically isolated from the tank 10 by the non-conductive, liquidenergetic substance 12 and possibly other non-conductive material. Suchother non-conductive material may include paint, coatings, rust, and/orsludge. Electrical isolation may also occur if the mobile platform 100is partially or completely immersed in a non-conductive, gaseousenergetic substance 14 inside the tank 10. When encountering suchelectrical isolation, the rate of electrical charge dissipation from themobile platform 100 may be lower than the rate of electrical chargeaccumulation, which may cause a relevant amount of electrical chargeaccumulation on the mobile platform 100.

Referring now to FIG. 22, there is shown a non-limiting embodiment of aretrieval system 1001 for retrieving a mobile platform 100 from a tank10 at least partially filled with a non-conductive, energetic substance12, 14. As described below, the retrieval system 1001 may be used toreduce and/or minimize this charge accumulation before or during theretrieval of the mobile platform 100 from inside the tank (10) tooutside the tank (10).

The mobile platform 100 to be retrieved may be configured to include anenclosure 200, a control unit 300, a propulsion system 400, and a powersupply 500. These components and sub-systems have been already discussedabove and will not be described in further detail. A generic electricalpower consumer is shown with numeral 1330, which is representative ofany device that consumes electrical power, including but not limited to,the control unit 300, the marker detector 306 (FIG. 4), the dynamicsensor 380 (FIG. 13), the propulsion system 400, the task module 600(FIG. 2), and/or any device not described in the present specificationthat consumes electrical power. As noted previously, the configurationof these components and sub-systems are not limited to any previouslydescribed embodiment, e.g., the enclosure 200 need not be inherentlysafe and the mobile platform 100 may be used in conjunction with acarrier (not shown), which may be a passive or active carrier. Also, twoor more enclosures may form the enclosure 200, with each of theseseparate enclosures acting as housing structures for differentcomponents. Moreover, other mobile platforms may include additionalcomponents or fewer components.

The mobile platform 100 also includes a retrieval module 700 disposed atleast partially on the enclosure 200. That is, the parts making up theretrieval module 700 may be internal and/or external to the enclosure200. Also, some parts may be embedded in a wall or body of the enclosure200. In one arrangement, the retrieval module 700 may include a buoyantbody 702, a tether 1100, and an electrically conductive member 1300. Theretrieval system 1001 further includes a voltage differentialneutralizing body 1302 and an electrically conductive cable 1304.

In one embodiment, the tether 1100 connects the buoyant body 702 to theenclosure 200, the tether having at least a portion that is notconductive. Because the tether 1100 electrically isolates the buoyantbody 702 from the enclosure 200, proximity or contact with the buoyantbody 702, or the tether 1100 near the buoyant body 702, will not form anelectrical connection between the buoyant body 702 and the enclosure200. That is, at least a portion or section of the tether 1100 issufficiently not conductive to prevent a transmission of electricalenergy between the buoyant body 702 and the enclosure 200. The buoyantbody 702 is similar to that previously described. In configurationswhere the tether 1100 is fully submerged in the non-conductive, liquidenergetic substance 12, the tether 1100 may not need to have a portionthat is not conductive.

The electrically conductive member 1300 may be an object, body, plate,coating, or structure that is electrically connected to one or moreregions on the enclosure 200. The electrical connection is sufficient totransfer some, substantially all, or all of the electrical chargeaccumulated in and/or on the enclosure 200 to any electricallyconductive object in electrical communication with the electricallyconductive member 1300, assuming the appropriate voltage differentialexists. The voltage differential neutralizing body 1302 may be anobject, device, body, plate, coating, or structure into which anelectrical charge can be discharged. In some arrangements, the tank 10or ground 30 can act as the voltage differential neutralizing body 1302.The electrically conductive cable 1304 may be a conventional cableconfigured to transmit electrical energy between a neutralizing body end1306 and a mobile platform end 1308. In embodiments, the electricallyconductive cable 1304 may include an insulating outer sheath (notshown).

Referring now to FIG. 23, there is shown a conveyance device 1310 forconveying the mobile platform end 1308 of the electrically conductivecable 1304 to the electrically conductive member 1300 on the enclosure200 of the mobile platform 100. The conveyance device 1310 may be aharness, ring, sleeve or other suitable sliding member that can slidealong the tether 1100. The conveyance device 1310 has sufficient mass topull the mobile platform end 1308 downward to the electricallyconductive member 1300. The mobile platform end 1308 may include asuitable connector 1314 that electrically connects to the electricallyconductive member 1300. There may be a direct physical connectionbetween the connector 1314 and the electrically conductive member 1300or an indirect connection that allows electrical communication. Theelectrically conductive member 1300 is shown as electrically connectedto one localized region of the enclosure 200. However, in embodiments,the electrically conductive member 1300 may be in electricalcommunication with two or more discrete regions of the enclosure 200 atwhich electrical charges may accumulate. Referring to FIG. 22, theneutralizing body end 1306 of the electrically conductive cable 1304 mayinclude a suitable connector 1316 that electrically connects to thevoltage differential neutralizing body 1302. Likewise, the connectionmay be a direct physical connection or an indirect connection.

While illustrated as single, unitary bodies, it should be understoodthat the described devices, including, but not limited to the buoyantbody 702, and the tether 1100, the electrically conductive member 1300,may be formed of two or more separate portions, sections, or segments.Further, as discussed previously, components of the mobile platform 100,such as the enclosure 200, may be formed of two or more separateenclosures.

Additionally, some variants of the retrieval module 700 of FIGS. 11A, Band 19 include a primary tether 1100 that is constructed to be buoyantin the liquid energetic material 12. For example, the primary tether1100 may include one or more materials that make the primary tether 1100positively buoyant in the liquid energetic material 12. Alternatively oradditionally, the primary tether 1100 may include buoyant bodiesdistributed along the length of the primary tether 1100. In suchvariants, the buoyant body 702 is considered integral with the primarytether 1100.

FIG. 24 illustrates a non-limiting embodiment of a retrieval method 1400according to the present disclosure that employs the retrieval system1001 of FIGS. 22 and 23. The method 1400 may be of particular use whenthe tank 10 is at least partially filled with a non-conductive,energetic substance 12, 14. At step 1402, the mobile platform 100 to beretrieved may be configured as shown in FIG. 22. However, the method1400 may be used to retrieve other mobile devices not described in thepresent disclosure.

At step 1404, the mobile platform 100 is lowered into the tank 10 usinga deployment carrier 50 (FIG. 16A). Other embodiments may use thedeployment carriers 764 or 780 (FIGS. 11C, 11D, respectively) or othersuitable systems for lowering the mobile platform 100 into the tank 10.At step 1406, the enclosure 200 is submerged in the non-conductive,liquid energetic substance 12. If two or more separate enclosures arepresent, then only one of those separate enclosure needs be submerged.Moreover, the enclosure 200 does not have to be fully submerged; i.e., apartially submerged state may be suitable in certain instances. Itshould be noted after step 1406, some components used in conjunctionwith the mobile platform 100, such as an active or passive carrier (notshown) may not be submerged. At step 1408, the mobile platform 100 ismoved using the propulsion system 400. The movement may be in connectionwith performing an assigned task or some other function. At step 1410,which may be at or near the conclusion of completing the assignedtask(s) and/or function(s), the buoyant body 702 is released to conveythe tether 1100 toward a surface 1116 of the non-conductive, liquidenergetic substance 12.

step 1412, the electrically conductive cable 1304 is conveyed to theelectrically conductive member 1300 of the mobile platform 100 using thetether 1100. At step 1414, the neutralizing body end 1306 of theelectrically conductive cable 1304 is connected to the voltagedifferential neutralizing body 1302 in a “spark inhibiting ambientcondition.” As used herein, a spark inhibiting condition is a conditionwherein ambient conditions in which the connection is being made aresufficiently deficient in oxygen and/or an energetic substance topreclude a spark from igniting an energetic substance, if such anenergetic substance is present.

At step 1416, the mobile platform end 1308 of the electricallyconductive cable 1304 is connected electrically to the electricallyconductive member 1300 of the mobile platform 100 while the electricallyconductive member 1300 is below the surface 1116 of the non-conductive,liquid energetic substance 12. A fully submerged condition is considereda “spark inhibiting ambient condition” due to a suitable deficiency ofoxygen.

In conjunction with the execution of steps 1412, 1414, and 1416, theconnector 1314 may be conveyed to the mobile platform 100 using thetether 1100 and connected electrically to the electrically conductivemember 1300. Depending on the system used, an exemplary method mayinvolve retrieving the buoyant body 702 with a retrieval member 1110,attaching an electrically conductive mobile platform end 1308 of theelectrically conductive cable 1304 to the tether 1100, and sliding theelectrically conductive mobile platform end 1308 along the tether 1100to the mobile platform 100. Thereafter, the electrically conductivemobile platform end 1308 is connected electrically to the electricallyconductive member 1300.

At step 1418, the mobile platform 100 is retrieved from inside tooutside of the tank 10.

In variants, personnel may first estimate when a voltage differentialbetween the mobile platform 100 and the tank 10 is below a predeterminedvalue and thereafter retrieve the mobile platform 100 from inside tooutside of the tank 10. The predetermined value may be a voltagedifferential that cannot generate a spark capable of igniting one ormore energetic substances in or around the tank 10. The estimation maybe based on measurements, theoretical calculations or modeling, and/orhistorical information.

FIGS. 25A,B are flow charts depicting other sequences for electricalconnection of the electrically conductive cable 1304 to the voltagedifferential neutralizing body 1302 and the electrically conductivemember 1200.

In FIG. 25A, the steps 1414 and 1416 are be performed in reverse order.That is, step 1416, wherein the mobile platform end 1308 of theelectrically conductive cable 1304 is connected electrically to theelectrically conductive member 1300, can be performed before step 1414,wherein the neutralizing body end 1306 of the electrically conductivecable 1304 is connected to the voltage differential neutralizing body1302.

In the FIG. 25B method, the initial step is step 1414, wherein theneutralizing body end 1306 of the electrically conductive cable 1304 isconnected to the voltage differential neutralizing body 1302. Next, step1412 is taken, in which the electrically conductive cable 1304 isconveyed to the electrically conductive member 1300 of the mobileplatform 100 using the tether 1100. Thereafter, step 1416 is taken, inwhich the mobile platform end 1308 of the electrically conductive cable1304 is connected electrically to the electrically conductive member1300. Finally, at step 1418, the mobile platform 100 is retrieved frominside to outside of the tank 10.

As discussed previously in connection with the embodiment of FIG. 22,when the mobile platform 100 is operated in an environment that createselectrical isolation, the rate of electrical charge dissipation from themobile platform 100 may be lower than the rate of electrical chargeaccumulation, which may cause a relevant amount of electrical chargeaccumulation on the mobile platform 100. FIGS. 10 and 26 illustratenon-limiting embodiments of a mobile platform 100 that uses a chargeaccumulation control system (CACS) to reduce and/or minimize this chargeaccumulation or the rate of increase of this charge accumulation priorto and during retrieval of the mobile platform 100.

In the FIG. 10 embodiment, a switch assembly 250 for communicating withthe mobile platform 100 is described as configured to shift betweenpower states, activate or de-activate sub-systems, initiatepre-programmed instructions, etc. Near or at the end of operations, theswitch assembly 250 shifts to the “off” position, which shuts down themobile platform 100. The shutdown of the mobile platform 100 effectivelystops the relative motion between the non-conductive, liquid energeticsubstance 12 and the at least a portion of the mobile platform 100contacting the non-conductive, liquid energetic substance 12 while themobile platform 100 is inside the tank 10 and prevents any such relativemotion later while the mobile platform 100 is inside the tank 10 andalso terminates the supplied power and prevents a reengagement of thesupplied power later while the mobile platform 100 is inside the tank10.

FIG. 26 illustrates another CACS 1003 for controlling a chargeaccumulation between a mobile platform 100 and a tank 10 at leastpartially filled with a non-conductive, energetic substance 12, 14. Themobile platform 100 may be configured to include an enclosure 200, acontrol unit 300, a propulsion system 400, and a power supply 500. Thesecomponents and sub-systems have been already discussed above and willnot be described in further detail. A generic electrical power consumeris shown with numeral 1330, which is representative of any device thatconsumes electrical power, including but not limited to, the controlunit 300, the marker detector 306 (FIG. 4), the dynamic sensor 380 (FIG.13), the propulsion system 400, the task module 600 (FIG. 2), and/or anydevice not described in the present specification that consumeselectrical power.

The mobile platform 100 also includes a retrieval module 700 that has atether 1010 connected to a buoyant body 702. The tether 1010 may be anyof the tethers described in this disclosure or any other connectingcable, line, rope, or wire. The configuration of these components andsub-systems are not limited to any previously described embodiment,e.g., the enclosure 200 need not be inherently safe and the mobileplatform 100 may be used in conjunction with a carrier (not shown),which may be a passive or active carrier. Also, two or more enclosuresmay form the enclosure 200, with each of these separate enclosuresacting as housing structures for different components. Moreover, othermobile platforms may include additional components or fewer components.As discussed previously, components of the mobile platform 100 may beformed of two or more separate structures. Thus, while illustrated assingle, discrete components, it should be understood that the enclosure200, control unit 300, and power supply 500, buoyant body 702 may beformed of two or more separate portions, structures, sections, modules,or segments.

To control charge accumulation, the mobile platform 100 may include theCACS 1003, which may be operationally integrated into the mobileplatform 100. By operationally integrated, it is meant that the CACS1003 can, either cooperatively with the control unit 300 orindependently, control the operation of sub-systems that initiatemovement of the mobile platform 100, such as the propulsion system 400,and/or the delivery or the utilization of electrical power bysub-systems, such as the power supply 500 and control unit 300,respectively. The CACS 1003 may be a component or module of the controlunit 300 or a structurally and functionally separate device.

In an embodiment, the CACS 1003 may be configured to control anaccumulation of electrical charge on the mobile platform 100. Controlmay be exerted to reduce a rate of increase in the charge accumulationor reduce a total amount of accumulated charge. The CACS 1003 mayinclude a microprocessor programmed with suitable algorithms,application, or programs and circuitry to transmit control signals basedon processed data, which may be pre-programmed and/or acquired duringoperation. The data may relate to operational data such the timeduration of operation, amount of power consumed, time spent moving, dataacquired, estimated time to completion of a task, etc. The data may alsobe acquired using sensors such as voltmeters. Based on pre-programmedcriteria, the CACS 1003 transmits control signals to the sub-systemscontrolling movement of the mobile platform 100 and/or one or moreelectrical power consumers onboard the mobile platform 100. As usedherein, the term “control signals” includes energy waves (e.g.,electrical signals, magnetic signals, optical waves, etc.) as well asphysical movement (e.g., translation, rotation, etc.)

In response to the control signals from the CACS 1003, the sub-systemthat receives the control signal(s), or “receiving sub-system,” shiftsto an operating state that uses less power. By operating at a lowerenergy state, the rate of increase of charge accumulation on the mobileplatform 100 may be either arrested, reduced, or reversed. The controlsignals may also cause the receiving sub-system to not return to anoperating state that requires a higher power consumption. For example,the control signals may instruct the receiving sub-system to not returnto the prior operating state or to an operating state that requireselectrical power exceeding a predetermined limit. As noted in connectionwith the embodiment of FIG. 10, the control signal may physicallyreconfigure an electrical circuit to prevent signal/power transfer whilethe mobile platform 100 is in the tank 10.

The CACS 1003 may also be configured to provide an indication thatcharge accumulation control is occurring or will occur after apredetermined time period; i.e., provide an indication of an activationstate of the CACS 1003. In one arrangement, the CACS 1003 releases thebuoyant body 702 to provide an indication of the activation state.Personnel and/or machinery can detect the presence of the buoyant body702 visually or by another method such as monitoring for audio signals,light signals, vibrations, etc. In the embodiment of FIG. 10, actuationof the switch assembly 250 shifts the entire mobile platform 100 to anon-operating state while simultaneously releasing the buoyant body 702.Thus, the presence of the buoyant body 702 at or toward a surface 1116of the non-conductive, liquid energetic substance 12 indicates topersonnel and/or machinery that the mobile platform 100 is in anon-operating state. The position at or toward the surface 1116 of thebuoyant body 702 and attached tether 1010 is shown in hidden lines. Invariants, the buoyant body 702 may be released before chargeaccumulation control occurs. In such instances, presence of the buoyantbody 702 indicates that charge accumulation control will occur afterexpiration of a predetermined time delay (e.g., ten minutes, thirtyminutes, an hour, etc.) or other measurable parameter (e.g.,quiescence). In other variants, the buoyant body 702 may be releasedafter charge accumulation control has been initiated. In theseinstances, presence of the buoyant body 702 indicates that chargeaccumulation control is presently occurring.

Thus, by detecting the presence of the released buoyant body 702 insidethe tank 10, personnel may estimate a magnitude of the electrical chargeaccumulation on the mobile platform 100 and retrieve the mobile platformafter the estimated magnitude of the electrical charge accumulation isbelow a predetermined value. Depending on the situation, the presence ofthe released buoyant body 702 may indicate that the magnitude of theelectrical charge accumulation is below the predetermined value or thatthe magnitude of the electrical charge accumulation will be below thepredetermined value after expiration of a predetermined time durationafter the presence of the released buoyant body 702 has been detected.The predetermined value may be a voltage differential that cannotgenerate a spark capable of igniting one or more energetic substances inor around the tank 10. The estimation may be based on measurements,laboratory testing, field tests, theoretical calculations or modeling,and/or historical information.

Referring to FIG. 26, in some embodiments, the CACS 1003 may alsoinclude an electrical charge dissipater 1500 and an actuator 1502. Theelectrical charge dissipater 1500 is configured to discharge anelectrical charge accumulated on the mobile platform 100 to a voltagedifferential neutralizing body 1504. The electrical charge dissipater1500 is shown as electrically connected to one localized region of theenclosure 200. However, in embodiments, the electrical charge dissipater1500 may be in electrical communication with two or more discreteregions of the enclosure 200 at which electrical charges may accumulate.The voltage differential neutralizing body 1504 may be the tank 10, thenon-conductive, liquid energetic substance 12, and/or an object 1506positioned inside the tank 10. When activated by the CACS 1003, theactuator 1502 extends, drops, exposes or otherwise electrically engagesthe electrical charge dissipater 1500 with the voltage differentialneutralizing body 1504. This electrical connection may reduce theelectrical charge accumulation on the mobile platform 100 and therebyreduce a voltage differential between the mobile platform 100 and thevoltage differential neutralizing body 1504.

FIG. 27 illustrates a flow chart of one non-limiting embodiment of aretrieval method 1600 according to the present disclosure that employsthe CACS 1003. At step 1602, the mobile platform 100 to be retrieved maybe configured as shown in FIG. 27. However, the method 1600 may be usedto retrieve other mobile devices not described in the presentdisclosure.

At step 1604, the mobile platform 100 is lowered into the tank 10 usinga deployment carrier 50 (FIG. 16A). Other embodiments may use thedeployment carriers 764 or 780 (FIGS. 11C, 11D, respectively) or othersuitable system for lowering the mobile platform 100 into the tank 10.At step 1606, the enclosure 200 is submerged in the non-conductive,liquid energetic substance 12. If two or more separate enclosures arepresent, then only one of those separate enclosure needs be submerged.Moreover, the enclosure 200 does not have be fully submerged; i.e., apartially submerged state may be suitable in certain instances. Itshould be understood that the enclosure 200 need not be completelysubmerged in the non-conductive, liquid energetic substance 12; i.e.,“submerged” does not mean that the entire enclosure 200 is immersed inthe non-conductive, liquid energetic substance 12. It should be notedafter step 1606, some components used in conjunction with the mobileplatform 100, such as an active or passive carrier (not shown) may notbe submerged. At step 1608, the mobile platform 100 is used to performone or more tasks in the tank 10. At step 1610, an activation state ofthe CACS 1003 is indicated by releasing the buoyant body 702 toward asurface 1116 of the non-conductive, liquid energetic substance 12. Atstep 1612, the CACS 1003 controls the accumulation of electrical chargeson the mobile platform. At step 1614, the mobile platform 100 isretrieved from inside to outside of the tank 10.

FIG. 28 depicts a method that reverses the steps of charge accumulationcontrol and indication of such control activity. Specifically, thecharge accumulation control step 1612 occurs before the step 1610 ofreleasing the buoyant body 702. As noted previously, the two steps canalso occur simultaneously.

FIG. 29 is a flow chart depicting details of steps that may be performedduring the charge accumulation control step 1612. The steps 1616, 1618,1620 are intended to reduce a rate of increase of electrical chargeaccumulation, maintain a level of accumulated electrical charges, orreduce the amount of accumulated electrical charges. Steps 1616 and 1618may be considered “passive” in that performance of these steps controlssources contributing to electrical charge accumulation, but not theelectrical charge accumulated on the mobile platform 100. Step 1620 maybe considered “active” in that performance of this step changes themagnitude of the accumulated electrical charge on the mobile platform100. These steps may be taken independently or together in anycombination. At step 1616, control signals or some form of actuationreduce or stop motion that contributes to electrical chargeaccumulation. At step 1618, control signals or some form of actuationreduce or stop power usage that contributes to electrical chargeaccumulation. For both of steps 1616 and 1618, a return to the priormagnitude of motion or power usage is prevented unless acted upon by aninput that is external to the mobile platform 100. That is, an actor,whether human or machine, that is external to the mobile platform 100must take an action, e.g., transmission of a signal or manipulation ofsome form of switch or other actuator, to allow a return to the priormagnitude of motion or power usage. At step 1620, the electrical chargedissipater 1500 is actuated to discharge some or all of the accumulatedelectrical charge on the mobile platform 100 into a voltage differentialneutralizing body 1504.

It is emphasized that the above described embodiments and relatedmethods are only illustrative of some embodiments of the presentdisclosure. Other systems and related methods may use an active carrierin conjunction with a mobile platform and may not use an inherently safeenclosure and incorporate one or more features described in connectionwith FIGS. 2-29.

By “conductive” or “electrically conductive,” it is meant an electricalconductivity greater than 100 microsiemens per meter.

By “electrically isolating” two objects, it is meant that the electricalresistance between the two objects exceeds 1 mega ohm.

By “charge accumulation” or “electrical charge accumulation,” it ismeant the exchange of electrons between two objects resulting in eithera positive or negative voltage differential increasing between the twoobjects.

By “charge dissipation,” it is meant the exchange of electrons betweentwo objects resulting in either a positive or negative voltagedifferential decreasing between the two objects.

By “not conductive” or “not electrically,” it is meant an electricalconductivity less than or equal to 100 microsiemens per meter.

An “energetic substance” is any material that is considered to be atrisk of igniting or burning. In certain applications, an energeticsubstance has one or more of the following properties: (i) anAutoignition Temperature (AIT) of 700° C. or less, (ii) a flashpoint of150° C. or less, (iii) a Minimum Ignition Energy (MIE) of 1.5 mJ orless, and/or (iv) a Minimum Ignition Current Ratio (MICR) of 1.5 orless.

An AIT is the minimum temperature required to initiate or causeself-sustained combustion of a material independently of the heating orheated element. A flashpoint is the minimum temperature at which aliquid gives off vapor in sufficient concentration to form an ignitiblemixture with air near the surface of the liquid at standard atmosphericconditions. A MIE is the minimum energy required from a capacitive sparkdischarge to ignite the most easily ignitible mixture of a gas or vapor.A MICR is the ratio of the minimum current required from an inductivespark discharge to ignite the most easily ignitible mixture of a gas orvapor, divided by the minimum current required from an inductive sparkdischarge to ignite methane under the same test conditions. A MESG isthe maximum gap of the joint between the two parts of the interiorchamber of a test apparatus that, when the internal gas mixture isignited and under standard atmospheric conditions, prevents ignition ofthe external gas mixture by flame propagating through a 25 mm (984 mils)long joint, for all concentrations of the tested gas or vapor in air.

Energetic substances can be dust, particulates, slurries, solids,liquids, vapors, gases, and combinations thereof. Examples of energeticsubstances include, but are not limited to, coal dust, hydrocarbonliquids, fuel oils, and gasoline.

“Burning” is the chemical reaction that takes place when an energeticsubstance is ignited. Burning encompasses combustions, explosions,detonations, and deflagrations. “Ignite,” “ignited,” and “igniting” meanapplying energy of a sufficient quantity to an energetic substance tostart the chemical reaction. A “spark” is a thermal event having atleast enough energy to ignite an energetic substance. The term “thermalevent” includes sparks and sparks caused by explosions. A “combustible”material is a material that undergoes a chemical change that producesheat and light when ignited. A “flammable” material is a gas, liquid orsolid that ignites and continues to burn in air if ignited.

It is emphasized that the present teachings can be readily applied to avariety of industries and uses beyond tank inspections, whether aboveground or underground. Thus, the described systems and methods are onlyillustrative of how the advancements of the present disclosure may beimplemented. For example, mobile platforms according to the presentdisclosure may be used in connection with storage units and containerscarried by barges, tankers, railroad cars, or ships.

The foregoing description is directed to particular embodiments of thepresent disclosure for the purpose of illustration and explanation. Itwill be apparent, however, to one skilled in the art that manymodifications and changes to the embodiment set forth above are possiblewithout departing from the scope of the disclosure. Thus, it is intendedthat the following claims be interpreted to embrace all suchmodifications and changes.

We claim:
 1. A method of operating a mobile platform in a tank at leastpartially filled with a non-conductive, energetic substance, the methodcomprising: configuring the mobile platform to include at least: anenclosure, at least one control unit positioned in the enclosure, atleast one propulsion system at least partially positioned in theenclosure, at least one electrical power supply positioned in theenclosure and configured to supply electrical power to at least oneelectrical power consumer associated with the mobile platform, whereinthe supply of electrical power is capable of adding an electrical chargeto the mobile platform, at least one retrieval system disposed at leastpartially on the enclosure and including at least one buoyant body, andat least one charge accumulation control system disposed at leastpartially on the enclosure, the at least one charge accumulation controlsystem being configured to control an accumulation of the electricalcharge on the mobile platform by one of: (i) reducing the supplied powerand preventing an increase in the supplied power later while the mobileplatform is inside the tank, and (ii) disengaging the at least oneelectrical power consumer from the supplied power and preventing areengagement of the supplied power with the at least one electricalpower consumer later while the mobile platform is inside the tank;lowering the mobile platform into the tank using a deployment carrier;submerging the enclosure in a non-conductive, liquid energeticsubstance; moving the mobile platform using the at least one propulsionsystem to perform at least one task in the tank; controlling theelectrical charge accumulation on the mobile platform using the at leastone charge accumulation control system; indicating an activation stateof the charge accumulation control system by releasing the at least onebuoyant body from the enclosure, the activation state being one of: (i)prior activation of the charge accumulation control system, and (ii)activation of the charge accumulation control system after apredetermined time delay; and retrieving the mobile platform from insideto outside of the tank.
 2. The method of claim 1, wherein a relativemotion between at least a portion of the mobile platform and an adjacentsurface adds an electrical charge to the mobile platform, and whereinthe charge accumulation control system controls the electrical chargeaccumulation by one of: (i) reducing the relative motion and preventingan increase in the relative motion later while the mobile platformremains inside the tank, (ii) stopping the relative motion andpreventing the relative motion later while the mobile platform remainsinside the tank.
 3. The method of claim 2, wherein the adjacent surfaceis at least one of: (i) a contact surface of the non-conductive, liquidenergetic substance, and (ii) a surface of a wall of the tank.
 4. Themethod of claim 1, further comprising: detecting the presence of thereleased buoyant body inside the tank; estimating a magnitude of theelectrical charge accumulation based on the presence of the releasedbuoyant body inside the tank; and retrieving the mobile platform frominside to outside of the tank after the estimated magnitude of theelectrical charge accumulation is below a predetermined value.
 5. Themethod of claim 4, wherein the presence of the released buoyant bodyindicates that the magnitude of the electrical charge accumulation isbelow the predetermined value.
 6. The method of claim 4, wherein anexpiration of a predetermined time duration after the presence of thereleased buoyant body is detected indicates that the magnitude of theelectrical charge accumulation is below the predetermined value.
 7. Themethod of claim 1, wherein the tank is at least partially separated fromthe non-conductive, liquid energetic substance by a non-conductivematerial.
 8. The method of claim 7, wherein the non-conductive materialis at least one of: (i) paint, (ii) a coating, (iii) rust, and (iv)sludge.
 9. The method of claim 1, wherein the charge accumulationcontrol system includes an electrical charge dissipater electricallyconnected to the mobile platform and an actuator configured to actuatethe electrical charge dissipater, and further comprising: electricallyengaging the electrical charge dissipater with a voltage differentialneutralizing body using the actuator, wherein the electrical chargeaccumulation on the mobile platform is controlled by electricallyconnecting the mobile platform to the voltage differential neutralizingbody using the electrical charge dissipater.
 10. The method of claim 9,wherein the voltage differential neutralizing body is selected from oneof: (i) the tank, (ii) the non-conductive, liquid energetic substance,and (iii) an object positioned inside the tank.
 11. The method of claim10, wherein the enclosure includes a plurality of separate enclosures,and at least one enclosure of the plurality of separate enclosures issubmerged in the non-conductive, liquid energetic substance.
 12. Themethod of claim 1, wherein only a portion of the enclosure is submergedin the non-conductive, liquid energetic substance.
 13. The method ofclaim 1, wherein a portion of the mobile platform is not submerged inthe non-conductive, liquid energetic substance.